The storyteller generally stands out from the rest of the sound by bring in a quiet room an optimal distance from a good quality microphone and no background noise. Sometimes the Sound Designer will add just a pinch of theme music underneath. Yes compression will be handy gently applied because you don't want the announcer volume all over the map, but you don't get that storyteller presentation with compression alone.
If you pull that off just right, the voice can be used as a bridge between two different scenes with different sounds. That's why the storyteller has to be neutral and in a quiet environment.
One of the people here did a movie with a storyteller and he got it exactly right. He would take each scene right up to some awkward silence and then the storyteller would break in with some perfect bit of dialog to carry you to the next scene. I think they shot it in a bedroom with moving quilts and mattresses piled against the walls for soundproofing.
It was falling down funny.
I don't think they used compression at all.
Koz