i'm sure you're right that it's not necessarily the case, but from experience i find it's pretty likely. i think RiB has much more in common with DM primarily, so maybe that would be the next step, and then there's DM which comes close to BM, etcetc. i'm not trying to say you *should* like black metal if you like RiB, i just think anyone who likes metal would more than likely reap many rewards from giving every one of its sub-genres quite a bit of time and effort, giving them the opportunity to get past any initial distractions, expectations, biases etc.
as an aside, i think sometimes people dismiss genres for different reasons; namely misinformed perceptions of what those genres entail. like for example i used to associate hard rock with glamour, flashy solos for their own sake, sleaze, etcetc so i stayed the hell away from it, but exposing myself to more of it made me realise just what a ridiculous generalisation that was (and i think it's one a lot of people share). god, some of that stuff is so dark and epic and visceral and mesmerising, i have no doubt that most metallers would love it if they gave it a chance.
i think with black metal, if some people associated it with the same feelings i associate it with, that'd probably make it far easier for them to get past the vocals, because they'd really want to get past them. i know that's how it was for me once upon a time - when i started reading all these reviews making it sound so fucking cool, i made an extra effort trying to understand how they found all these images and moods in the music, because to me it just sounded like ridiculous noise. in time, i did understand.
i suppose my underlying point is that it's best for the listener to approach all music with as little resistence as possible. if you still can't get anything out of it after a while then fine, no point wasting your life, but if you keep resisting stuff for one reason or another without really trying to get into it then you're gonna miss out on a whole lot, especially if the music in question is a sub-genre of a genre you've already got a lot out of.