Bah DRG doesnt have the heavy equipment to take the hits. They have paper thin armour and are there to deal damage. The Defense Boosts arent enough really and if theres another boost that is the same as you main job, they dont stack at all. So DRG stay away from long term tanking. The only time you should Provoke is when your doing a Trick Attack with a main tanker job(PLD, WAR, NIN).
You(DRG)>>>>Mob<<<<PLD<<<<THF
The THF will Trick and Sneak Attack right behind the PLD and Bam, all hate goes on PLD and then he will provoke to generate maximum hate. PLDs are the best at keeping hate.
Although more so then anything, in the party the tank should be the guy with provoke, the most HP and defense, that way he can live long.
In the case of the PLD, high MP also helps, because Cure/Flash spells generate hate and they use it so no one else gets hit. They also have Shield Bash and Sentinel to help them.
A WAR however, the high HP counts more because you have less of a means to keep hate unlike a PLD/WAR(which is the only viable combo). Warcry helps, but in the end your all around, dmg dealer and tanker, but not the most ideal one to most.
A NIN however, HP matters very little, they can cast Utesumi(Blink) on themselves multiple times to absorb hits and Provoke with their /WAR subjob. They however as efficient in taking hits, cannot hold hate well so others have to hold back a bit.
Despite the different tanks and the way they achieve the same means, the THF trick attack still applies and can help alot. However DRK, DRG, THF, SAM, and MNK arent the ideal tanks, they can sorta do it til lvl 30(and even then its worst than the real tanks), but afterward they will take too much damage and waste WHM and RDM MP.