I was a physics background doing a non-physics startup. (Not anymore, cofounder took over my share) I think having a physics person as a cofounder or in the initial few hires is a decent idea. The STEM background is there, but with a slightly different outlook on the universe than, say, other STEM fields. For example, you get a little of the classic "Don't say 'reflected acoustic wave.' Say echo!" attitude. (Well, I mean I guess you can get that attitude anywhere, but I see it more often with physics people)