Received wisdom has it that ethernet ports in things like switches are "transformer coupled" so there shouldn't be any direct pathway between mains currents and the conductors in the attached UTP cables. One presumes the ethernet ports in HomePlugs (and TV's and everything else) are similar.
Possibly, but everything is built to a price. The transformer coupling would certainly provide the necessary isolation, but with budget products there's no way of knowing if that technology has been used, unless the kit is disassembled.