I don't master the VDDK but I have a general knowledge from the experience I got from a Third Party VM backup/replication software.
STEP1 :Snapshot created - all writes goes to delta
STEP2:Copy base disk
STEP3:Copy base Disk finished - consolidate delta
These are not the exact steps but i understand it in this way.
All the steps are carried via the VDDK calls.
now my question : is it possible to check if the parent disk is locked before consolidation ? This check should be made just before STEP3.