Re-grinds on camshafts are fine and return the shaft to original lift and duration. The lost material is taken up in the valve lash adjustment. Be sure to ask them if they heat treat (or nitride?) the camshaft after the re-grind. I have seem to remember reading that that the re-grinding process can cut through the thin layer of heat treatment on original camshaft.

I agree old gear meshed to new gear is not an issue.