Hmmm two power hungry, controlling people in a relationship? Especially one with an extensive murderous history? I see issues. Just saying, Sylar would need someone a little more...easy going.

Well, If the both wanted the same thing they could be partners perhaps. But I don't see a relationship between them. If they both like being in control that means one of them won't be, which they would not like. It's not possible.

Well, now you mention it they might be quite a cute couple and have their moments... But, two controlling, power-mad people that like to get their own way? Maybe not. Say they moved in together, what if they decorated their house? What if one wanted teal walls in the hall wheras another wanted pale yellow? They'd end up trying to kill each other, probably succeding!