yes in fact if you do what you need to unlock an armor in co op you unlock that armor for both files or players i tried this and now me and my brother both have same armors for unlocking armors in co op well almost all sometimes i play with out my brother. all armors are unlock able in co op but also if you are playing co op and you find a skull both files or players get the skull. i did not know this till i did what i took to unlock a armor in co op.
beat campaign on legendary
No, in Halo 2 you can not unlock armor.
The only way to get armor on ODST is to unlock it on campaign . Except recon wich you need Halo 3. By Mr. Happy Guy.
You unlock the armor.
You unlock the odst armor by unlocking the UNSC SPARTAN achievement
You have to be an warrant officer in halo reach to unlock the helmet you also have to go to halowaypoint and unlock the armor.
go to http://hubpages.com/hub/Halo-3-Armor
scout armor is only for looks
Unlock Halo 3:ODST's Campaign Complete Achievement. Once you beat the ODST campaign, visit Halo Waypoint on the dashboard to unlock the item.
To unlock Recon armor in Halo 3, you originally had to beat all of the VidMaster achievments, but the armor is now available to all players. To unlock the recon armor in Halo: Reach you had to pre-order the game and you would get a long (25 character) code for the recon armor DLC. To unlock the recon armor in Halo 4, you had to either pre-order the game or simply buy the armor with your in-game credits.
Get sculls or get achievements
All of the regular armor can be unlocked by beating the campaign on legendary and collecting all skulls. You can get the Katana (sword) on your back be getting the origanal 1000 gamerscore. There's also recon armor, which can only be unlocked if Bungie (the makers of Halo) give it to you.