I dont think this is a surprise to anyone but here it is.
just got the September Edition of OXM and they have confirmed more Spartans for Halo 3 although they are AI controlled!
This is a quote from the magazine " The Chief is not to be messed with, and neither are the other spartan super soliders in the game. Halo 3 marks the frist apperance of the class of bionic warrior outside the Halo novels. We often thought Master chief might be the last one left, but in Halo 3 we saw plenty of new ones in halo 3, Some look very similar but there infact different configurations of the Mjolnir battle armour, You will be able to customise your apperance in multiplayer, but in Campaign mode you will see the armour being worn by AI contolled spartans.
Dont know if this is old so sorry if it is but its new to me!