The secondary benefit to running biopellets is the healthy amount of bacterioplankton that develops in the water column. I believe the UV, if strong enough with proper flow through, would eliminate this. On an ULNS the bacterioplankton feed your corals, without it I believe the potential for coral stress is high. Now on the other hand, I run Biopellets And 8x57w UV stacked consecutively above the return pump with great results, but there are no corals in that system.
Hope that helps
Sean