The details provided in the interview don't address the question entirely, but we do know that the first DLC pack will cost 320MSpts and will feature two new arenas & three new cars. Here's where the uncertainty comes in: does this mean the DLC is already done before the game ever launches? We're not big fans of that sort of thing if true, but given that this is an XBLA game there could be a number of reasons for it. The most likely would be limited storage size, the other would be desire to keep the entry price lower. Oh well, we'll probably never know anyway.
Gallery: Vigilante 8 Arcade (XBLA)