We don't know if Hellbindi took the oath. Also why do we need to tell Hellbindi?I think they were hired with PF so we can use the jotunheim branch to let Hellbindi know. Even if they weren't hired with PF the branch could still let Hellbindi know since he'll be bound by oath.
@KnowledgeKing does Loki have the knowledge to do the magic oath that we took on someone else?