I can't speak specifically about the SD38, but I have a SD45 that I run on 042 curves without any problems. I have never tried it solo, only in a multiple unit consisst. I think it will work if the car it is coupled to has articulated couplers and sufficient weight to keep it on the track.
Here is a video of my SD45 coupled to a GP35. I apologize for the poor video quality. I was trying to follow the consist around the layout while focusing on the pilots.
Tom