Remember those space bunnies that usually pop up in Orbulon's microgames? Well they appear in Rhythm Tengoku for the GBA, the Remix 8 minigame I believe. They also appear in Working Dough 2 in Beat the Beat Rhythm Paradise / Rhythm Heaven Fever and supposedly in Remix 2 in the DS game. Are they cameo games or are they not?
Game & Wario features ton of Rhythm Heaven cameos, most notably the Chorus Kids in the intro and the Reporter / Wrestler in the intro of one of the minigames. Either way, it's clear to me the two series are in the same universe.
Maybe we'll see the WW developers cameo in the next Rhythm heaven? : o
Kind of like why DK Vine doesn't count Sabrewulf GBA as a cameo game. Same sort of feel, likely the same universe, but nothing that pushes it past the 'similar style' line.
On the subject, there's supposedly a cameo of Young Cricket in Rhythm Heaven Fever, and at first glance it does look like him. However....
this guy has grey hair and different eyes. Not only that, but since Game & Wario used the Rhythm Heaven artstyle Young Cricket still looks different from this guy.