Captain Metropolis, Hooded Justice, and The Silhouette were the homosexual members of the group.
I knew about Hooded Justice, but where does it say those other two were as well?
Check the Sally Jupiter interview right at the last page of the Chapter IX supplement. Sally explicitly states that "the papers got hold of... her being a gay woman," in reference to the Silhouette.
Later, when asked who else was gay, Sally doesn't name anyone, but says "it was a couple of the guys and they're both dead now. One died recently, I'm not saying who it was." We know Hooded Justice was one of them, so that leaves one more. Nite Owl and Mothman are ruled out because they are both still alive at the graphic novel's start. The Comedian is out for obvious reasons.
That leaves Dollar Bill and Cpt. Metropolis. But Metropolis was killed in '74 (Chapter I, pg. 19, panel 4) and the Sally Jupiter interview took place only two years later (September 1976, check the lower left-hand corner of the interview).
Dollar Bill, on the other hand, died well before Hollis Mason wrote his book. Otherwise, his death couldn't have been mentioned in said book (page "8" of the Chapter II supplement). And Hollis mentions the book in Chapter IX, page 11, panel 8, when Metropolis is not only alive -- he's in the panel!
So, the second gay man is almost assuredly Cpt. Metropolis.
(I love having my book back.