This is a great question, and I'm glad you brought it up. My thoughts are in line with torachan's. If someone familiar with the source text (or in the case of RPF, the publicly-known biography of the person in question) would know that a given character is a sexual or gender minority -- or you could find that out with some quick Googling -- then letting that be implicit seems fine. But if there's interpretation involved, I'd like some cue in the work to indicate that. Again, authorial discretion applies; I'm not saying there needs to be sign-waving ("Okay, so go straight at the light--" "Honey, I can't go straight, I think you mean gaily forward"). I think a good test would be: if you encountered that work in a neutral context, and you were someone with the same minority identity as the character in question, would you put it down afterward with a quiet feeling of recognition?

Is that helpful at all?