It could prove bad, but not if you remember that it is just a dream. If you start thinking it is really him it could prove... Well bad.

Personal experience:
DCs either think they are real, dreamers, or spirits. Rarely do they think that they are not real and just figments of your imagination.

If you talked to him and he convinced you that he was real (DCs are really freaking tricky if they want to be) then he could be in a position to traumatize you. A lot of times they will "prove" something to me that when I wake up makes absolutely no sense. Now as long as when you wake up you are confident that it is just a dream, even if he persuaded you it was real in dream, then you should be fine. Gotta be confident in what you believe in about dreams.

I have had DCs convince me that I wasn't dreaming and that I was dead a few times. That is weird. Haha. Next time I might have to check out heaven. I also had a DC point to a flower and say that because that flower is there, it is a shared dream. I have no idea how that made perfect sense to me.