By the way, I just wanted to add that this is what I mean when I say that Vox and Charlie are extremely similar, even though Vox is way more dysfunctional. They're both neglected children who are starved for approval and recognition. And while they're both surrounded by a supportive network of people, they both hyperfixate on ONE person whose approval really matters to them (Alastor and Lilith). They're both scared of failure and they both want to meet the expectations of the one person they admire, but I also think, and we'll see if season 3 confirms this, that they both have idealised these two people. They know them, but they don't actually know them, you know what I mean? But when they finally do, they'll inevitably go through a phase of disillusionment and disappointment with Alastor and Lilith, and that'll actually be a good thing, because you can't build a solid and healthy relationship without honesty and clarity.
Anyway, once you analyse Vox's obsession with Alastor in this perspective, you see how it's clearly not just about sex. It goes way deeper than that and it touches themes like self-worth, self-esteem, emotional neglect, starvation for approval, need for guidance, and desire for a deeper connection.
From what the canon material has shown us, I think Vox wouldn't rape Alastor because he would gain nothing of true relevance to him by doing that. Yes, exhibitionism still counts as SA, but even that was just Vox's fucked up way to show off his prowess. Yes, the song is full of sexual metaphors and imagery, that's clearly something Vox (maybe not so) subconsciously wants, but that's not the core of his desire. The guy BLUSHES like a goddam virgin when Valentino even suggests him and Alastor should fuck. He can threaten and allude, but he's fucking bashful about the reality of it. Because Vox doesn't see Alastor just as a sexual object, but as a person with thoughts, ideas, and opinions, and those are the things that he ultimately cares about the most.
Which is why I think they could work in an asexual relationship, once they set aside their rivalry. Yes, Vox is sexually attracted to Alastor, but he loves and admires him for his personality, his fucked up creativity, his tastes, his style, his ideas, his confidence, his humour. And he's not the kind of man who just wants mindless sex. He likes it, sure, but I don't think it's essential to him.
In short, if canon Vox had two magic buttons, one that would make Alastor sexually subservient and always available to him, but also indifferent and emotionally closed off, and another button that would make Alastor see him, appreciate him, like him and be his friend, but never in a sexual way, he would totally smash the second button. At least that's what I see in the canon material.