What, of Enterprise's main cast? No, the only one of them who isn't shown to be definitively heterosexual is Phlox, who might be bisexual/pansexual given in A Night in Sickbay he makes a comment implying (rather obviously, at that) that he's been involved with some of his wives' other husbands. But based on Archer's reaction to that, it seems to Archer anyway heterosexuality was considered the norm among 22nd century humans. Which I always found especially odd, given Bakula was one of the more vocal during Enterprise's run about how there should be a gay character on the show.