Howdy
Yes, Belt Mountain base pins will fit Ubertis. I have put them in Colts, Rugers, and Ubertis.
I do recommend staying away from the pins with the little set screw. Too much torque on the set screw can warp the pin just enough to bind the cylinder. Plus, you have to keep that tiny allen wrench handy if you want to take the cylinder out at the range. If the pin is properly fitted, it should stay in place without a locking screw even with the heaviest recoiling loads.