I play Warhammer ONline but I don't know which code you mean. They gave it at least 5 different codes.
They had Collectors Edition items which I got for buying the beautiful CE version which is one of the best CE's next to EQ2's tin imo.
For people that already had Mythic account's from playing Dark Ages of Camelot, they gave an item for Warhammer ingame.
Then if you buy the EZ Board Warhammer version you get another item that helps recharge action points quicker.
Then their's the standard preorder hiwch gives the campfire and rings.
If they gave one away for playing UO then I don't know about it and I don't know how that would work since UO's accounts go under EA subscriptions and Warhammer's/DAoC goes under Mythic. Unless I'm wrong here.
Need more info maybe.