I have never tried to turn it, but, for what it's worth my opinion is, yes plexiglass should be turnable. My first job out of grad school back in "68" was with Rohm and Haas, the original manufacturer of plexiglass. Plexiglass, at least back then, was poly methylmethacrylate, a pretty basic acrylic. It is not the hardest material and is (was) scratchable. That should not be a big problem if thin slices are used as accents.
Larry