No, they don't. Fully demonetized videos don't run ads because that's the entire point of demonetization - that the video was deemed unsuitable for showing ads

No, they don't. Fully demonetized videos don't run ads because that's the entire point of demonetization - that the video was deemed unsuitable for showing ads (because ad buyers don't want their ads showing next to certain content). Partially demonetized videos may show ads, but from a reduced set of advertisers - those videos will make money but possibly not as much due to less desire for the ad space on that content.