Does UP still use the short cut across the lake?
Yes.
Dave H. Painted side goes up. My website : wnbranch.com
Yes, its currently operates as part of Union Pacific's Lakeside Subdivision division. There has been some traffic changes there ever since UP adopted PSR, as many of the priority trains that used to run straight between Ogden and Elko have been downgraded to lower priority runs, taking the slower Shafter Subdivision (former Western Pacific) through Salt Lake City then back up to Ogden. A few years ago UP completed a program to build a new bridge on the Causeway to help balance the salinity between the northern and southern arms of the lake: https://www.up.com/aboutup/community/inside_track/causeway-6-14-2016