I see your points, that a framework might be there for an ace option and that he says things that might hint towards that direction.
However, and this is based on my experience romancing him a couple times just to get different dialogue options, when he's the most honest with you, it really does seem he's hinting more at being demi/pan than ace.
His whole thing is that he has no agency or choice over his actions. His body is used for someone else's gain and so sex becomes a second nature to him and as a result, holds significant trauma over his life. This is grounds for it holding no appeal for him which could open the ace route.
However, he explains that in the beginning of his tasks to seduce people, he enjoyed it. He explained he thought it would be fun having sex with people all the time and that for a time, it was. But he slowly realized he was being abused with no option to fight back.
This speaks less to a person who doesn't want sex/doesn't have sexual urges and more to a person that is sexually traumatized and that, at this point, needs a more emotional connection to enjoy sex and have it be on his terms. That's why he might be more demi than ace, in my opinion.
That doesn't mean he couldn't benefit from someone who's asexual helping him through his trauma but I don't think he'd think it was romantic unless there was an element of them helping him enjoy sex on his own terms again.
Because sex is clearly important to him. He just doesn't know how to do it without it being for manipulation.
