I didn't like in Halo 4 how the UNSC treated Masterchief with less respect then past games. It seemed they didn't even care that the last Spartan who saved humanity was actually still alive.
At the start and end of Forward Unto Dawn, it seemed they cared, as Lasky was listening to Cortana's signal multiple times, and the radios were blaring about Masterchief being alive and stuff in the background. Then in the full game, I don't even believe they mention Chief being gone. Literally the first line the UNSC say to chief, is Palmers brilliant line of "I'd thought you'd be taller." srsly yo?
But yes, to an extent, It is basically like Halo 3 never happened in Halo 4.