Yes, PMMA is what Bellafill uses to create volume. I can be used in the butt (I haven't) however it would require a very large amount. This becomes not economically feasible for most people. Sculptra will last 5-7 years or more in this region.
Yes, you can use it for butt lifts however the volume is very small. It all comes down to the cost benefit ratio. Most specialist will use their own formulation of Sculptra. This provides the most amount of volume with the lest expense (relatively speaking in context of no- fat transfer fillers). All the best, Davin S. Lim