I recently purchased the Skyrim Dawngaurd DLC on one of my household's two xboxs on my gamertag.  If i were to download it on my gamertag on the other xbox could all gamertags on the second xbox use the DLC or not?  Would i have to transfer my gamertag's license to the second xbox for it to work?  Also if i did this, would i still be able to play the DLC on the first xbox?
I've numbered your questions to make responding easier.
 On the other Xbox, the DLC will only be usable when your profile (the purchasing one) is signed in to Xbox Live on that console.
 Yes, if you transfer all your gamertag's licenses to the other console, profiles that aren't yours can use all your content whether your profile is there or not, and whether there's an Xbox Live connection or not.
 If you transfer your licenses to the other console, your profile can still use all your DLC on the first console (or any other console) as long as you are connected to and signed in to Xbox Live. (This means that the License you are transferring is effectively the offline license.)