Generally speaking, mux chips (video, audio, whatever) do not switch the ground, and require that all signal have a common signal ground potential. Maxim makes some nice parts; they are the basis for many video mux boxes on ebay. With proper decoupling and a little input filtering, is should not be the case that a bunch of floating connections fro the circuit GND act as noise antennae. I've dealt with large video switching arrays in TV stations and not had a problem.
ak