objectGuid LDAP attribute can be sent as the value of any claim by using "Send LDAP Attributes as Claims Rule" and specifying
objectGuid as the source attribute. ADFS has no specific knowledge of LDAP attributes, and if you were to extend your LDAP schema, you could use those just as easily as any other. The particular claim you must transform it to is mandated by the relying party.
If you are just using it as the user's unique ID, you might send it as
Private Personal Identifier), but you might also send it in a claim specific to your particular RP (which is when you would need to add a claim description).