Considering the fact the all of multiplayer is a simulated experience that takes place on the UNSC Infinity, it would have to mean that every aspect of the Halo 4 multiplayer’s simulation is canonically linked to the ship’s capabilities. This (canonically speaking) means that the announcer’s voice must already exist in the ‘real world’ outside of the simulated multiplayer space.
I’m not saying this is the case, but it would be a pretty neat idea to see the announcer as a character aboard the Infinity. Maybe even, the ship’s AI?