To answer this you have to have a generally accepted definition of "gay". Dictionaries notwithstanding, I'm not sure this truly exists. Ennis sure didn't think he was "gay", but he knew what he liked and what pushed his buttons, from the SS:
"Sure as hell seem in one piece to me. You know, I was sittin' up here all that time tryin to figure out if I was_? I know I ain't. I mean, here we both got wives and kids, right? I like doin' it with women, yeah, but Jesus H., ain't nothin like this. I never had no thoughts a doin' it with another guy except I sure wrang it out a hunderd times thinkin' about you. You do it with other guys, Jack?"
He wasn't afraid to tell Jack that his fantasies were not only him, but sex with him. I think this shows a lot of self realization and, for Ennis especially, confidence about his sexual desire (in order to share this with Jack). Note I said desire not desires, it seems pretty specific to Jack, period.