If your character is seventeen feet tall and would squish a human simply by giving them a single-digit high five, yes, they'll need to magically shrink down to Earth-people size to fit aboard. You can blame the Mysterious Recruiter for leaving that out of the sign up spiel.

"Too inhuman" is likely variable, given that it's deep space with other planets, but if you need to humanize your character so that others don't run away screaming, we give you the thumbs up. Let us know if you need any specific feedback for a particular character you have in mind.