Yes, but Heinlein sucks*.
In all seriousness though, Halo is the biggest collection of sci fi action clichées ever devised. It just got them in the right order such that people liked it rather than loathed it. The large majority of those have been covered by Cameron, regardless of whether he created the concept. A Halo movie by Cameron would be Aliens with Ripley swapped out for the Chief and Cortana. And that is why Cameron will never do it.
Inspiration =/= Ripping Off. Enough with the Avatar bashing. We all know it was a pretty poor movie excluding the technical achievements of its production.
*It's a joke, don't worry.