Short Answer - No.
Longer Answer - The Ultra Slug and the 10 ga are built on the SB2 shotgun frame, not to be confused with the SB2 rifle frame. The frame is larger than the standard shotgun/huntsman frame. It's not supposed to work and NEF will not fit the barrel to that frame. However I have read on GBO of people that are using regular barrels on the SB2 shotgun frame. Kind of a crapshoot if you ask me.