In addition to what Lisa and I found together, Chaim himself has said that he always believed him to be so because he has the mannerisms, persona, presence, etc. of a "butch" or masculine sodomite. He said that he viewed him as being very similar to known homosexual J. Edgar Hoover. No Chaim isn't clairvoyant but I would say his record of people-reading is pretty darn good. My guess is that he is at least bi.
I would be really surprised if he were straight.