In workstation mode the "/opt/quest/bin/vastool isvas user username" command should work correctly. Any user which is not in the cache will be added to the cache when that command is run. To see if the user is cached run "/opt/quest/bin/vastool list user username"
If the "/opt/quest/bin/vastool isvas user username" is not returning and it should be an unix identity attribute (homedirectory, UID, GID, shell) or the user principal name (UPN) for the user may not be filled out.
To check AD attributes on the account use "/opt/quest/bin/vastool -u host/ attrs username"