Give it a try - simple enough, just disable S Voice and see it your BT dialing with PIN lock engaged works. I'm guessing that this is not a carrier issue, but an S Voice programming issue . . . but then again, anything is possible.
Try Settings --> My Device (tab on top) --> Call --> Call Accessories --> Outgoing call conditions and then the choice of actions should be obvious.
This will ONLY (Verizon S4) work if you disable S Voice first. Then the Google dialer will take charge and allow BT voice dialing even if the lock...