Yes, you can actually. There are 13 skulls in all. If you collect all of the skulls you will get hyabussa armor.
You unlock the odst armor by unlocking the UNSC SPARTAN achievement
beating the campaigne on legendary is a fast way of unlocking most the armor. some achievemnets also unlocks armor.
http://hubpages.com/hub/Halo-3-Armor
No, there is no armor in Halo 3 that has a knife in the shoulder.
There is no Brute armor in Halo 3, only Elite and Spartan models.
go to http://hubpages.com/hub/Halo-3-Armor
you get all the vidmaster achievements on halo 3 and halo 3 odst
NO
recon armor
the same way in halo 3 because when you play halo 3 mythic it says your playing halo 3
there is no permanent cheats in halo 3. you need to unlock them by achievments. and, you can not get the flaming armor effect, it is only for bungie employees. in halo reach, buy the legendary package to get that armor effect.
Hayabusa