I very much doubt he kept anything from her. Dracula is literally the Lord of Darkness, the Satan if you will of Castlevania's universe.
I do wonder about this. When you think about it, if Dracula would have been completely frank about past, that would bring up several awkward moments that would be... a bit of a turn-off in a relationship (and that would be putting it lightly). If we break this down just for fun, we can list the following details Lisa would know about Dracula:
1) He is a vampire. This wouldn't necessarily be problematic assuming vampires in the Castlevania universe can survive without human blood. But if that's not the case, that would make him a potential serial killer.
2) He manipulated, lied to, and betrayed his former best friend. He also indirectly made him kill his soon-to-be wife. His motivation for this was purely selfish.
3) He later tried to have this friend killed after the latter refused to join him in eternal life.
This would be on top the fact that Dracula is also an evil wizard who uses black magic, the type of magic used for personal gain and detriment of others, and the fact that he associates himself with beings with clear malicious intent to humans.
For all I know I could be wrong and none of this matters to Lisa, but it kind of seems like a hard sell when thinking about this in a story writing way. It almost feels a bit forced, and makes it seem like Dracula just needs another dead wife he can mourn over in order to become the villain. I suppose that is kind of the point of Lisa's character (which in itself is a bit of a tired trope), but that doesn't mean the romance between her and Dracula could be made to be understandable to the audience. This aspect of the timeline (pre-1476) is not very well explored but it could lead to some interesting story possibilities, I think.