Today, I take on a team of former Covenant troops (who were recently recruited into The Banished) on The Ark. The said troops have yet to get their new armor, and must defeat an "intruder" to attain it. However, you'll quickly see WHY they're "former" Covenant troops. XD
Pardon my terrible aiming, these vehicles I used clearly weren't meant for the players. However, it's odd that they aren't usable in stock Halo 3, since you can access all of their functions just from a controller alone (with the exception of the Scarab's AA cannon). :P