Using an UPS to minimize RFI is possible if you have good grounding in your electrical system. However, it may also make no difference in regards to RFI.
What an UPS will do is protect your PC in the event of a power outage. I use UPSs for all of my systems.
The bottom line is that you have a 50/50 chance that it help with your RFI issue (better insulated/shielded cabliong is your best best here). Good luck!