That's a good question. First, I don't think the state matters. The basic question is really whether or not there is a conflict of interest. I think it's a question of fine degrees largely judged by what document is being notarized.
I would prefer that the real estate agent, wishing to avoid any potential conflict of interest, would not act as a notary for any reason on their own deal. In reality, we live in a world in which many real estate agents are steeped in conflicts of interest in every transaction and they seem to have little respect for ethical lines drawn in the professional sand.
So, unless and until all the more substantial conflicts of interest, such as dual agency, are resolved, who the hell cares?