Is it better to undistort in Mocha or use an already undistorted plate if available?

If there is an undistorted plate and distortion maps from CG already available, should i go ahead and use those from the start to track in Mocha Pro?

If you’re relying on an external calibration for the existing render, then I’d recommend using that. There’s no use doubling up on work.
You can either import STMaps to define the lens calibration in Mocha or alternatively just work with the undistorted footage and reapply your distortion later.

The main reason to use Mocha for the lens calibration is that it tracks into the existing distortion, but if you’re already working in a flattened space and plan to redistort later, you might as well just use the undistorted source that you have.

Unless of course you’re doing something like 360 work.