The above mentioned quest is currently available only to Rogues while in fact it should be available to all playable classes.
Thinking that this is definitely a DB issue, I talked to the people at YTDB (forum post: http://ytdb.ru/showthread.php?t=3697) but as YuruY told me everything is in working order DB side and that it is a core problem.
In short descritpion: Quest is currently given by Fahrad (NPC 6707) for Rogues only since, as YuruY told me, from WDB => `ZoneOrSort` = '-162' which means that it is for rogues only as he said and WDBs taken from the official WoW also confirm that `ZoneOrSort` = '-162'. On the official WoW, all classes can take and complete this quest. WDBs taken from official WoW can be found in the forum post above and YuruY made sure that the quest data in YTDB is like data taken from official WoW.
Bug is still present as of MaNGOS rev9509, using YTDB R537.