Nope. As long as it functions.
Example: Complete DPMS rifle, obviously the upper and lower should have matched machining (coming from the same factory) that permit them to operate together.
Now, same DPMS lower, and say you buy yourself some billet upper that's supposed to be DPMS format - if that thing doesn't run, you'd need to look at the machining on that upper, very first, make sure it's right - then move to gas system issues.
We've seen it happen, right here. Guns that don't run right, and upper and lower are made by the same company... One company comes to mind on that. We've seen a BUNCH of mix-n-match stuff that won't run, either. Different people machining, based on what they think the pattern is... It ends up not really an "Apples and Oranges" thing. More of an "Apples and Hammers" thing... <lmao>