The lag isn't just on NA_Siege it's on other NA servers as well, even duel.  It just effects siege much worse than the other servers so it's less noticeable.
I talked to some admins and they say it's not on the servers side but on game databases side.  I have no clue how the servers work so i could be wrong with that.
Some word from chadz or any other developers would be nice though if the lag is being caused by the game database.