Hold on.
It MAY be "working as intended" to be able to disenchant if an enchanter is in your group even if they aren't present/eligible for the item being disenchanted. (This makes a certain amount of sense. Say it's a "unique" epic being DEed. Having it work this way gives the group the benefit of their enchanter who wouldn't be given the "need or greed" roll dialogue.)
However, the exploit here is having an enchanter in a separate party within a raid group. For instance, someone in Group 3 in a 10 man, Group 6 in a 25 man or maybe even group 2 in a 5 man. The person is not intended to be able to influence the people who are in the dungeon in any meaningful way.
"Not working against game mechanics" is not necessarily "working as intended". If you don't see a difference between the two, I'm curious what you'd define an exploit as. The way I see it, the whole (and sole) criteria for being an exploit is getting a reward that goes against the spirit/design intent of the game code but which the letter of the law or actual coding permits you to do.
If the code doesn't ordinarily permit you to do it (even with some odd behavior on your end) then it's hacking, not an exploit. If it doesn't go against the standard design goals as we generally see them in some way (ie. giving people in an instance a benefit from someone not in the instance), it's also not an exploit.
This is probably the purest and most replicatable exploit on the first five pages of MMOwned's WoW exploit forums. It gives a reward/benefit. It can be tested. It doesn't require excessive tricking/modifying code/doing weird things to your UI OR social engineering.
This is the perfect example of an exploit.
+Rep