Can any stylus be used on the ipad pro?

Depends, are you talking about simple tapping or a full featured stylus?

If the former most likely. If the latter, as in does an Adonit or Wacom top of the line stylus work, then you may get a better answer by turning to those manufacturers. I am sure they are testing the compatibility of their devices with the new iPad.

I Imagine any stylus that works with a capacitive touch screen will work but just not be able to take advantage of the iPad pro's new screen features or the high resolution touch of the Apple pencil. It's still just a capacitive touch screen at heart, just with new enhanced features for pressure sensitive touch.

The $ is most likely worth it depending on what you need it for. When iPad Pro senses Apple Pencil, the subsystem scans its signal at an astounding 240 times per second, giving it twice the data points it normally collects with your finger. This data, combined with Apple‑designed software, means that there’s only milliseconds between the image you have in your mind and the one you see on the display.

Also with the Apple Pencil it has pressure sensors, capable of measuring a range of forces. The carefully positioned sensor determines precisely how hard the tip of Apple Pencil is being pressed down. Press harder to draw thicker lines. Or use a gentle touch for wispy hairlines.

A 3rd party stylus will not have the same scan rate or pressure sensors.