Add a CUCM User/Extension from another server cluster to a line group/hunt pilot?

Hey Guys,

My company has two CUCM servers that services different remote offices around the world. I am tasked with adding some global IT members to a line group/hunt pilot that belongs to one of the clusters. Is it possible to add extensions that are a part of another cluster to a line group/hunt pilot? Users from both call managers can call each other just fine BTW.