I guess it would depend on how far the sub is from the point of termination on the wall where it would convert to a coax patch to the sub.
It actually doesn't depend on distance at all. The fact that the cable is terminated with a plastic connector introduces the risk of interference. Stray noise in the room (even from your lights or dimmer switches) can find its way through the plastic connector.
Don't worry, I'm convinced its a bad idea. However I do wonder. Since CAT5 doesn't really rely on the sheathing for any significant insulation from interference but actually relies on an electrical shielding effect produced by the the method and tightness of the twists in the wire, is it actually the removal of the twists at the termination point more so than the plastic that would create more risk for interference? That has been my schooling on CAT5 to this point in investigating interference on CAT5 structured wiring.
Note: This is a conversational question, not a defensive rebuttal as either theory makes cat5 a bad choice for audio where there is increased risk of electrical interference.
