I have completed the required achievement called "With a Little Help From My Friends", and am able to retrieve Hexid as a companion on all my other alts.
The only character I can't is a newly leveled Jedi Knight (post 6.0 expansion). When I enter the Collections and select Hexid, instead of the summoning holocommunicator going into my inventory, I get an email from "a deleted character" that has the holocommunicator in the attachments. I can't retrieve this attachment and can't have Hexid as a companion as the end result.