How did Allied soldiers who were Jewish, gay, etc react upon encountering concentration camps? Do we have any documents on their specific reactions, and their perspective versus soldiers not of targeted populations?

This is not my area of expertise, but I can direct you to a scholarly source. The National Museum of American Jewish Military History produced an exhibition in 2015 called GIs Remember: Liberating the Concentration Camps. There are several video interviews with Jewish-American liberators available from this exhibition, and many written interviews as well.