Brett Elston, Senior Online/Community Manager at Capcom Unity, posted today additional info about the Resident Evil 6 DLC situation. First off, he confirmed that two pieces of free DLC were coming soon: No Hope difficulty and a co-op partner for Ada Wong's campaign. The No Hope difficulty is only for those wanting to test their skill and willing to die over and over again. Ada Wong's campaign in the game will allow for players to play cooperatively with another player once the update has been downloaded.
Elston then explained that the free DLC is on-disc and may require either a download from Capcom when available or you heading to ResidentEvil.net to unlock it. On the other hand, the paid DLC is not on-disc and will be coming later on. That paid DLC would include the various multiplayer modes that they have planned.
Source: Capcom Unity