What happens is as the party is wiping someone raises someone dead that person waits and rezes before the instance boots everyone. if you dont move you will not draw aggro. Everyone raises and buffs and continues the fight where they left off.
Is this an exploit? I guess in the most basic of definitions it could be but then again using something to gain advantage is the most basic of definitions of exploit. In gameing the definition of exploit is "Using something to gain unfair advantage over others".
The so called exploit is useable by anyone so really I guess it comes down to morals an whether you care if anyone cares that you used said tactic.
Issues with said exploit is they make the fight longer and you run into the risk of running out of time, it actually happens quite often. And of course even with the reset you still have to defeat the moogle