This motor has magnets, though, so it is actually a DC motor, right?
Yep. AC would wreck the magnets.
I'm wondering why the manuacturer used a permag motor. I guess the plusses are that it won't overspeed when the load is light and it's probably lighter than an equivalent induction motor?
Correct. The PM motor will self-regulate speed, try to maintain speed under load and probably has more bottom end torque than an induction motor.
You might be able to have the armature rewound for 36 volts if you ask a motor shop nicely.
Chris