I don't see that working, how would the holograms hold weapons and such, and things like that.
I'm not opposed to the idea, I just want it to make sense, so this is what I think would work.
In a DLC to come it would be Spartan Ops Season 2 aka Elite Ops. The beginning would have the Arbiter coming in as he wants to deal with the elites personally. In doing so he brings a whole bunch of other elites who must train in War Games to keep in a good fighting condition.