So I'm home from college and picked up BF3. My 360 is still at my dorm, so im using my brothers console but with my hard drive, so my live account and data is on my hard drive but it's not my usual console. If I redeem the online pass with my account, will it not work when I bring my hard drive to a different console? Sorry if this is confusing, thanks!

If it's online it should.

It should as in it will work on my console in my dorm as well as my console at home? Assuming I have my hard drive/live account?

i believe online passes are tied to accounts and not hard drives

Yes, as opposed to something you buy and download off of XBLA an online pass simply activates your Gamertag to play that game online. Probably similar to how buying Live time does. So, if you activate your Gamertag on your brother's console as long as you use that same Gamertag to play at your dorm you should be fine.