Capcom will release Resident Evil 6 on October 2, 2012, and it's looking like Xbox 360-using fans are getting first crack at three pieces of planned, unannounced DLC. The official RE6 product page on the UK Xbox.com website notes that three "timed exclusive modes" will be released sometime after the game arrives, with more details to be confirmed at a later date (via CVG).
There's no similar mention of planned exclusive DLC for Resident Evil 6 on the US Xbox.com website, but that doesn't mean we won't be seeing the content as well. This follows the news from late August on Japan's Xbox 360 Twitter feed that RE6 DLC would be a timed Xbox 360 exclusive (via Kotaku). That's two territories now where we have confirmation straight from the source.
We've reached out to Capcom to confirm that the DLC is coming to the US as well, but I'd say it's a safe bet that it is.