If you are referring to the the VSA (Vault Service Account) then the answer is "No" to your question if you are using EV as designed.
Here is what I mean.
The VSA Windows credentials are used and not the VSA mailbox. You should use a system mailbox per exchange server (You can use one per mail store but you do not need to). The VSA will access the mail stores on each server using the system mailbox under the security context of the VSA.
This is why you have one VSA and many system mailboxes.
Other opinions are welcome on this one.
Jim S.