Should a cam button be used on a roller cam, and should a valve girdle be user on the valve train.

on a Mk 4 style yes. The Gen 6 has a special plate on the front to keep the cam in place and locks for the lifters.

Depends on cam. If you have a radical cam that requires heavy spring press or high rpm yes. If neither of those apply then no.

DAVE

From what you've posted in the past, you do not need stud girdles for your cam.

Gen V needs a cam button as well.