Can a regular 3 phase motor be controlled by an AC servo drive

Yes

answer says it all

I am thinking, if I can find a good deal on a AC servo drive, I might as well just put it on the spindle, would I get any advantages?

Sorry, I read your question wrong. AC servos and drives are different animals from three phase motors. Not compatible as far as I know.

karl

First, I think Karl's answer is too general. While some AC servo drives may accept induction motors without position feedback, many won't. Drives specifically set up for permanent magnet motors with commutation sensors certainly won't work with an induction motor.

Second, I don't think there would be any advantage. What do you expect to accomplish with this? Position holding like a C axis?

If you think it will make rigid tapping easier, I think i have proven it won't. Rigid tapping on my Bridgeport and minimill work amazingly well with no closed-loop spindle speed control at all. The Z axis syncs to the spindle, and as long as the spindle doesn't stall, it "JUST WORKS".

Jon

Spindle servos are handy when you need to do a spindle orient for an ATC, but that isn't applicable here.

No, but you can gain benefits with a VFD.