Hmmmmm. Some are, usually the more energetic end of the psychobilly spectrum, but any properly-constructed DB should be strong enough to support a bass player standing on the C-bout, which is (arguably) the most reinforced part of a DB anyway. And of course it helps (a lot) that rockabilly style normally keeps the end-pin all the way IN.
You can buy 'strengthened' DBs and you can retrofit reinforcement to an existing DB, but it's all a bit of a waste of time (IMHO). If you're going to treat a DB badly enough to risk physically breaking it somewhere important, then for the cost of the reinforcement you could just buy a cheap Chinese knock-off.
The last point is that if you or your bass or your band sound like **** then no amount of clowning about on the DB will rescue the gig. If you can play properly whilst performing crowd-pleasing tricks (I'm looking at you, @PaulKing) then well done that man ... carry on!