IP Camera and USB data transmission over Ethernet Cable
A USB cable already contains a ground, so there could be a potential for a ground loop which can create noise. If that is a problem, then you may want to consider isolating the 12V. 

USB should not be run over cables that do not have the proper tranmission line impedance. USB cables should have an impedance of 90Ω and twisted pair. Otherwise the error rate could go up significantly. USB should be ran in it's own shielded cable and not with other signals that could introduce crosstalk.