It seems like it should be, since you can set the Tileset independently on each Tile.
In practice, though, it seems to break. I have a Tilemap populated with Tiles using my “background” Tileset, and it works fine. When I add a character Tile using my “character” Tileset, however, things get weird: Many background Tiles don’t render at all, and the character Tile (when it renders) appears corrupted. The character Tile works if I remove the background Tiles, and the background Tiles work if I remove the character Tile.
Any ideas? I really hope I don’t have to squash all my assets into a single Tileset, but I need everything in the same Tilemap to properly layer things in the z-buffer.