Zargabaath's skills are interesting; definitely a support unit. I'm really not sure why Gumi is timing him to be released in succession right after 6* Tilith and Rikku; two amazing support units. Zargabaath is going to have to be amazing to justify his place on your team if you have either of the other two units.
Rejuvenate is basically Barts' Life Giver, its still not clear what the cost is however. Its obviously not going to be an instant KO, but if the MP cost is too high it could be just as expensive. Hopefully he also has something akin to a Curaja so that he can help heal as well.
Word of Law's damage mitigation is definitely unique, on GL we only have Sakura and Rikku that can cast an AoE version of it. For Rikku, you need two turns to set it up, and Sakura is still only a 5* unit. If his damage reduction is higher than Rikku's (30%) or his light attack is a multihit that can chain in with Orlandeau this could become a great unit.
Archadian Light is interesting, buff + status ailment resistance. Ramza is around the corner with 100% buff. If Zargabaath's buff isn't large it's going to be forgettable. It would have also been nice if he had something akin to a Full Break so that he could fill that role in support.
