Eric,
I will agree that MPR type V1 / VM will not trigger replenishments based on safety stock. However, ATP is not MRP. MRP type does not directly control ATP confirmations.
What is the requirements type in your Sales docs under PD/P1?
What is the requirements type in your Sales docs for V1/VM?
Do you have the same Availability check in your PD/P1 material masters as you have in the V1/VM material masters?
Best Regards,
DB49