Is the objectGUID unique and will it ever change?
http://technet.microsoft.com/en-us/library/cc961625.aspx?ppud=4
To copy and paste: SIDs can sometimes change. The SID for a Group object won't change. The values of other object properties can change, but the Object-GUID never changes. When an object is assigned a GUID, it keeps that value for life.
If there is a GUID associated with it, it should never change as GUID stands for Globally Unique Identifier