Hemi, If you've noticed on the track to the C&S yard, UP will keep a pair of SD40-2s parked from time to time. I've seen them coupled on the front of southbound BNSF freights for movement over UP (I'm guessing west to the ballast quarry at Granite).
Yes, they generally couple up to a BNSF ballast empty, headed west to load at Granite. Prolly for the special UP cab signals equipment not installed on BNSF units.