mostly free/pre order DLC can be used with any 360, not just JTAG's, or content that is made available via other means like a disc, eg the recent dragon age DLC content was accessible via USB methods because it was put on a disc .. same for the Fallout/Oblivion/Borderlands content packs.
the most important thing however is that you NEED the new title updates for the respective game if you're going to use new content for it.