You say he's under control of him, but...that's really not how it looks to me. I mean, when they fuse, you've said Vova gets Dracula's maddening bloodthirst and you made a point of saying there's pretty much no controlling him when he's summoned. As far as being a "prison" for him goes, I'm not entirely sure what you mean by that, but even ignoring the previous factors...the academy wouldn't allow it. In part because of the fact that Vova gains the thirst for blood if he's forced to fuse and in part because given the choice between having the powerful evil monster contracted to someone whose mental state he is capable of affecting and having the powerful evil monster not contracted to someone, they'd choose the latter.

I still don't agree with him being a dragon.