"An exploit, in video games, is the use of a bug or glitches, rates, hit boxes, or speed, etc. by a player to their advantage in a manner not intended by the game's designers."
http://en.wikipedia.org/wiki/Exploit_(video_gaming)
In the case of the Memory cloud it seems to me that you are not in fact exploiting the system because:
1. In order to get to the memory cloud you need to kill the bosses leading up to it and;
2. You need to actually do the fights in Memory cloud in order to roll on the loot.
3. Jade Citadel is by design split into sections to facilitate easier access to the later parts of the instance after killing the bosses to get there.
Does this in any way create an unfair advantage to anyone?
Well, it could be argued that in some ways it is an equalizer rather than a divider as it opens up possibilities for those not in a leading raid guild to access higher tier loots.