I've often sampled prog-rock and hard-rock (AC/DC type stuff) but never anything I'd consider 'metal'...
That's not to say I wouldn't; just that I've never chosen to.
If you have a metal sample that you think you can work into something that sounds dope - you should. No question.
Theres no real hard and fast rules to this shit. If it works for you - do it.
Just steer clear of that country & western shit - that don't fly.