I used to own a very large/popular websites and was very into the whole Adsense thing (generated over $1 million from 2006-2010) - i was even featured as one of Google's original "Adsense Success Stories" and knew/spoke with several Google/Adsense employees often.
The same question came up about websites being favored in Google search if they had Adsense ads on them, and the Adsense people made it VERY CLEAR - there was NO connection, or even communication between the adsense people and systems and the search people and systems. To the extent that they were not even allowed to speak with each other at lunch. Conversely, there was NO connection to ads and search results. The reason was because of the fear of monopoly issues, etc.
I dont know that the same separation exists in Youtube, but if would make sense for the same reasons if it did.