Actually, I see two possible problems with embedding these videos on a commercial web site. The first is that you may be violating the terms of use of YouTube by embedding content on a commercial site, rather than a personal blog - their policy strictly prohibits embedding videos for the purposes of advertisement.

Second, you don't have a fair use claim to the use of the background music because, unlike Google which only shows a representative, reduced copy of the media for purposes of demonstrating indexed content, you are using a full song as the background of what could be argued is an advertisement on a commercial site. I think in this case you are on a very fine line, and quite possibly over it.

In the case mentioned above, Google at least had a fair use claim: Google images displays reduced versions of the copyrighted material (thumbnail versions of full size images), for purposes of representing to users the contents of the full media file (the thumbnail has the purpose of giving a user a general idea of the contents of the full work, without actually showing the full detail of the protected work). This has been long held to be the basis for fair use in the US. I don't see any way that your proposed usage would fall under fair use exemption.

I almost read your original question as asking, "if I steal a song, can I get away with it because someone else hosts the stolen content, which was given to them by the person that originally stole it?" Just because you are the third party in the chain, you are knowingly and willlfully using the stolen content. If you got sued by the copyright holder, I can't see any possible defense you could use. It would be like driving around in a car that you know is stolen - it doesn't matter if someone else actually stole it, and it is stored in a rented garage, you're still going to jail.

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