Mike, yes the user-exit routines in MV45AFZZ will be called if you use any of the two BAPI's you mentioned.
I used BAPI_SALESORDER_CREATEFROMDAT2 and have code in "userexit_move_field_to_vbak" and "userexit_move_field_to_vbap" routines in MV45AFZZ.
-Chandra