A:
I connected 4 6ft of those once because I wanted to put a camera at my front door, and it worked fine.
I know you need to hire an electrician to mess with electric wires behind your wall so you don't violate any building codes, but I highly doubt a low power USB cable would violate any codes, if you are unsure, or care enough I would just call your local code enforcement office. Usually all they care about stuff that can cause fires, and USB cables can hardly do that, but dont trust me, im from the internet.