False info, they're totally the same data class. AD import modifies the Inv_OU_Membership dataclass, and is one reason why computers show as receiving an inventory recently even if they are not actually reporting a Software or Hardware inventory from Inventory Solution.
In any case, your information in Inv_OU_Membership will be outdated if you have disabled AD imports. You can select which computers AD import pulls in, so if you want only workstations, then uncheck the 'Servers' OU. If you want some servers but not others, and they reside in the same OU, then you will need to still import from AD, but not push the agent to these discovered-but-not-managed computers.
Alternatively, you could try working from the Inv_AeX_AC_Location table's 'Distinguished Name' field, but this is a little trickier.