1 - This may be possible if during the setup phase they download a little program which does a security check of the disk before allowing you to continue. You wouldn't even notice the download if the code is small enough.
2 - This would be a bit more involved and easily defeated by a switch or other measures. Again they would need to download some code to check out your bios. MS has also publically stated that they would NOT do this, whereas with item 1 they have stated that they will.
3 - It may be possible to spoof the verification of 1 & 2 but this is not trivial as they can encrypt the communication differently for each machine.
Furthermore Xblive MUST "makes it's way" thru your firewall for the games to play to begin with so anything which would block this short of active packet watching in Linux, would also block the game communication.
Remember for the most part all MS's servers do is initiate a PEER to PEER communication or a Client to Server communication amoung the XBoxes. Once a game starts XBLive falls away until you come back to the lobby.
Your Xbox is only talking to the player's Xbox at this point.