I've updated the original post in this thread to clarify my original statement. While normally you would only be able to play as the classes available in Gridania, please note that as a special exception during Beta Test phase 1 & 2, players will be able to complete specific objectives to unlock the gladiator class. Tanks will be very much needed for content like instanced raids (the level 25 dungeon in particular) and as such the dev. team has made them available for usage!
Eagle-eyed posters already spotted some gladiators in our most recent blog post, too.
Gladiator's Guild is on Uldah, the classes in Gridania are Conjury, Archer and Lancer. Plus the crafting classes are Carpenter, Leatherworker and Botany for Gathering.
Phase 3 is what I'm looking the most forward to. The lag in 1.0 was probably the greatest issue with the game since I was playing with 400 ms (other games like WoW and TSW had me anywhere between 70-150 ms), so it'll be nice to finally be able to check out the more localized servers. Also the NDA is lifted in that phase and anyone with an FFXIV account qualifies as a beta tester.