...To achieve SIL 3 Category 3 / PLe, STO would have to be used in conjunction with other Safety measures to achieve this higher Performance Level.
You need to know which Performance Level (PL) you require here before deciding whether or not it is permissible to use STO only on these drives.
That is, you may or may not need Safety contactors here. PLd, for instance, may permit the use of no contactors here...