https://en.wikipedia.org/wiki/Ukrainian_Insurgent_Army#UPA_and_Jews

There is a lack of consensus among historians about the involvement of the UPA in the massacre of Western Ukraine’s Jews. Numerous accounts ascribe to the UPA a role in the killing of Ukrainian Jews under the German occupation.[105][106] According to Ray Brandon, co-editor of The Shoah in Ukraine, “Jews in hiding in Volhynia saw the UPA as a threat.”[107] Other historians, however, do not support the claims that the UPA was involved in anti-Jewish massacres.[86][108]

While anti-semitism did not play a significant role in Ukrainian politics, the far right groups were anti-semitic like other nationalist and far right movements in Europe, with the first anti-semitic ideology and acts traced back to the Civil War in Russia. By 1940/41 the publications of Ukrainian nationalist and far right groups became explicitly anti-semitic.[109] German documents of the period give the impression that Ukrainian ultranationalists were indifferent to the plight of the Jews; they would either kill them or help them, whichever was more appropriate for their political goals.[110] According to John Paul Himka, OUN militias were responsible for a wave of pogroms in Lviv and western Ukraine in 1941 that claimed thousands of Jewish lives. The OUN had earlier repudiated pogroms but changed its stand when the Germans, with whom the OUN sought an alliance, demanded participation in them.[111] Recently declassified documents have shown that the OUN (Organization of Ukrainian Nationalists) was most likely not strongly involved in anti-Jewish activities in 1941.[112]

The OUN pursued a policy of infiltrating the German police in order to obtain weapons and training for its fighters. In this role they helped the Germans to implement the Final Solution. Although most Jews were actually killed by Germans, the OUN police working for them played a crucial supporting role in the liquidation of 200,000 Jews in Volhynia in the second half of 1942,[113] although in isolated cases Ukrainian policemen also helped Jews to escape.[114] Most of these police deserted in the following spring and joined UPA.[113]

Jews played an important role in the Soviet partisan movement in Volhynia and participated in its actions. According to Timothy D. Snyder, the Soviet partisans were known for their brutality, retaliating against entire villages suspected of working with the Germans, killing individuals deemed to be collaborators, and provoking the Germans to attack villages. UPA would later attempt to match that brutality.[115] By early 1943 the OUN had entered into open armed conflict with Nazi Germany. According to Ukrainian historian and former UPA soldier Lew Shankowsky, immediately upon assuming the position of commander of UPA in August 1943, Roman Shukhevych issued an order banning participation in anti-Jewish activities. No written record of this order, however, has been found.[116] In 1944, the OUN formally “rejected racial and ethnic exclusivity”[86]:474 Nevertheless, Jews hiding from the Germans with Poles in Polish villages were often killed by UPA along with their Polish saviours, although in at least one case they were spared as the Poles were murdered.[115]

Despite the earlier anti-Jewish statements by the OUN, and UPA’s involvement in the killing of some Jews, there were cases of Jewish participation within the ranks of UPA, some of whom held high positions. According to journalist and former fighter Leo Heiman, some Jews fought for UPA,[117] and others included medical personal.[118] These included Dr. Margosh, who headed UPA-West’s medical service, Dr. Marksymovich, who was the Chief Physician of the UPA’s officer school, and Dr. Abraham Kum, the director of an underground hospital in the Carpathians. The latter individual was the recipient of the UPA’s Golden Cross of Merit.[citation needed] Some Jews who fled the ghettos for the forests were killed by members of the UPA.[119]

One Ukrainian historian has said that almost every UPA unit included Jewish support personnel. According to Phillip Friedman many Jews, particularly those whose skills were useful to UPA, were sheltered by them.[120] It has been claimed that UPA sometimes executed its Jewish personnel, although Friedman evaluated such claims as either uncorroborated or mistaken.[121] But it has been said by historian Daniel Romanovsky that in late 1943, the commander of the UPA, Shukhevych, announced a verbal order to destroy the Poles, Jews and Gypsies with exception to medical personnel, and later fighters executed personnel also at the approach of the Soviet Army.[122]

According to Herbert Romerstein, Soviet propaganda complained about Zionist membership in UPA,[123] and during the period of persecution of Jews in the early 1950s described the alleged connection between Jewish and Ukrainian nationalists.[124]

One well-known claimed example of Jewish participation in UPA was most likely a hoax, according to sources including Friedman.[125][126] According to this report, Stella Krenzbach (pl), the daughter of a rabbi and a Zionist, joined the UPA as a nurse and intelligence agent. She is alleged to have written, “I attribute the fact that I am alive today and devoting all the strength of my thirty-eight years to a free Israel only to God and the Ukrainian Insurgent Army. I became a member of the heroic UPA on 7 November 1943. In our group I counted twelve Jews, eight of whom were doctors.”[127] Later Friedman concluded that Krenzbach was a fictional character, as the only data about her was published in an OUN paper. No one knew of such an employee at the Ministry of Foreign Affairs where she supposedly worked after the war.

Supporters of the UPA argue that the relationship between the UPA and Western Ukraine’s Jews was complex and not one-sided.[128]

The article also includes a photo of this apparently official UPA communication:

Ukrainian Insurgent Army, September 1944 Instruction abstract. Text in Ukrainian: “Jewish question” – “No actions against Jews to be taken. Jewish issue is no longer a problem (only few of them remain). This does not apply to those who stand out against us actively.”

I heard elsewhere that Karaite Jews were accepted by UPA, but Russian Jews were rejected as Moskals.

Karaite Jews believe more strictly in the Torah and do not feel bound by the oral traditions in the Midrash or Talmud. (https://en.wikipedia.org/wiki/Karaite_Judaism)

Interestingly, there’s a narrative suggesting it was Danylo of Galicia who invited the Karaites to settle there, though this narrative may have been invented to appeal to Rutherian sentiments. More here.