I have, lots of times. I non-lucid dreams, that is, so "run in to them" (but I often know them from before, being friends with them and so on). It's mostly characters from the Ace Attorney-games, but I've also met people from a few other games, Disneymovies and books. Also, a couple of times I've met my own fictional chararacters, from stories I've written, which is quite thrilling. I'd say the majority of these encounters, the characters have been very in-character.