Are crew members on Broadway?

From the stagehand's perspective, yes they are. Largely because the hourly rate for working at a Broadway theatre is much better than off-Broadway or television work. Though there's a difference between being on a show call (run crew) and a load in.

Of course they are, yes. The director isn't on stage either, but it would be insulting to tell them they're not really on Broadway if they've directed a Broadway show. All the musicians, stage managers, lighting, sound, wardrobe, directors, and anyone else I'm forgetting who are working on a Broadway show, are working on Broadway.

I am a member of Local 306 (the union that covers Broadway front of house staff.) I usher and am currently working at Hamilton. I think that it is fair for me to say that I work on Broadway. I"m clearly not a staff member at a non profit off Broadway house.