I don't really see any WarioWare characters fitting into Wario Land, especially if we're talking about the original games which had an edge to them, as opposed to Shake it!, and were pretty much solo treasure-hunts for Wario. Still, I could see them perhaps making Diamond City a sort of hub world if they were going to go that route. Have the WarioWare characters as NPCs that you can talk to, and do side missions for.
Buuuut I don't see them fitting in Wario's Castle in any way. That is known to be Wario's residence in the platformer games, and gave it a sense of continuity going back to the original Mario Land.