I've had two different replies on this from HQ.
One was he should only dive to his equivalent grade in the BS-AC, as there is no exact sign over and he's training to be a SD, then he should dive as an OD.
The other was he can dive to his grade outside of the bs-ac !
A DO's discretion/compromise may be to let him do the dive to 30m, but wih a DL or one of your experienced SDs.
hth
Paul