In theory, they could work. The problem area could be with the spindle's splines that mate with the crank arms. Are the machined splines, aka. (Wave taper interface) machined exactly to the SRAM standard? It is possible that visually they look similar, but due to SRAM patents, they have made slight changes, and might not properly fit in a true DUB or GRX based crank am. Crank arms could come lose, or get stuck on.
Specifically ask the seller if their spindle is 100% interchangeable with SRAM DUB or GRX
Also confirm if the axle lengths of 121, 125, and 129 are measured end-to-end, or outside-to-outside of the bearing surfaces.
I have been looking for 30mm diameter spindles that fit Race Face Cinch cranks since their prices doubled this year for OEM Race Face Spindles.