No, there was a crossover once

Ye, it was great, but does that make Layton an ace attorney character, or just a character in ace attorney???

It's confirmed that Layton and Phoenix don’t canonically exist in the same universe despite the crossover. Makes sense since PL is heavily implied to take place at a very different point in time than AA. So I don’t see why Layton should be considered an AA character. It would be like saying the characters in UMVC2 are AA characters for being in game with Phoenix.

I think that Ace Attorney characters who appeared in the crossover game also show up on the Layton wiki, and it is just because they were in the game. Even though the game is considered noncanon, I think it’s just an archive of ALL characters that have appeared in ALL games.

That being said, Takumi had said before that Ghost Trick and Ace Attorney take place in the same universe. However, as they do not share a game, they would not show up on each other’s wikis.