Brushless servos are basically AC induction motors, with their drives being more advanced VFDs.
Looking at the wiring, I'd say you should be able to drive your existing spindle motor using a VFD.
US, VS, WS will be the main power wires, SFAN will be the cooling fan power (you'd need to work out what voltage it needs), SPOH will most likely be a switch that breaks the circuit when the spindle overheats. The other connector will be the spindle encoder.
I'd be inclined to try a cheap VFD, and see if you can get the spindle to run. Even an undersized VFD should be able to spin up the motor to see if it will run, before spending money on a more suitable VFD.