I personally would keep the Ware cast out, or rather their world. Wario has never needed helpers.
Protip: Guide characters are helpers. Warioland 4 had a guide character(Shokora). Also, Syrup in Shake Dimension/Shake It was functionally a helper too, so no, Wario has certainly had helpers before.
Also, a Kirby 64 style helper system(outside Dedede) would be completely unintrusive and benefit the atmosphere of the game at no cost to the gameplay.