The OP's question was, if a patched ball was not seated firmly against the powder charge would damage result? The answer is it may. The issue of a ball not seating because of excessive fouling is a different question.
When I witnessed a drum blowing out from a ball not being seated was the result of fouling. The reason the event occurred was the shooter, as well as myself, knew almost nothing about shooting black powder rifles. It was 1968 and all I knew was what I read in a brief description about how to load a patched ball in a muzzleloader. Today we all have the benefit of resources such as this forum to accelerate the learning curve.
So, the first thing we should be advising someone new to the black powder shooting sport is to never intentionally shoot a ball not firmly seated on a charge (unintentional falls in the same category as dry balling or launching the ramrod). In my experience, the advice should have been to either pull the ball or hammer it down. Then, the next set of advice would be to swab between shots or, as you suggested, find the correct ball, patch and lube combination.
