So, though I'm sure he never tells chief in person, I think the contrast is pretty cool, and if they bother to show the players in reach, then next time they play halo 2/3 they will feel completely different about the arbiter.
The arbiter was the leader of the fleet that destroyed reach. He led the largest covenant force ever (next to truths fleet at delta halo) and destroyed the most important non-earth planet ever. He is responsible for killing more spartans, and probably more humans than any other elite (not personally, but he commanded the fleet). He's personally killed most of master chiefs family (spartans), the only people he ever felt a connection to.
I wonder just how chief would react if he knew the arbiter he was working along side with was the exact same elite that did this to his brethren.
I'm hoping bungie makes some reference to the arbiter in this game. Something to show how the one who wounded humanity more than any other covenant leader, was the exact same guy who was at the funeral at the end of H3, paying his respects to some of the people he was surely responsible for killing. This way we can see the stark contrast of the arbiter in H2/3, it will make his fall from grace and his eventual defection seem that much more significant.
And no, I don't mean play as the arbiter, but I'm hoping a scene or two where the arbiter is tasked with leading the fleet against reach or something. It will help tie it all together. To me, the chief you read about in the books feels completely different from the chief you play in the game, so anything to pull that together, is great to me.