I don't think that Dr. Wright is an actual playable character but more of a "environmental" effect on the stage or a power up of some type. Not sure how he'd be summoned though... Pokeball?

And it looks like Zero Suit Samus isn't a seperate character after all but after firing your super smash attack, your armor falls off and you're now Zero Suit. I don't know how I feel about that, but if Zelda/Shiek can work, I'm sure Armored/Zero Suit Samus will work fine too.

EDIT: Wright is an "assist trophy" along with Nintendogs and Hammer Bros. Pretty rad!