Know how when you are in a big building.. and you see fire hose hookups in the hallways or stairwells? They exist in the parks too.. they are just hidden. Sometimes in plain sight! There is a photo somewhere that illustrates this in one of the common disney books.. showing how they hid the fire hose hookup in a barrel that is painted with some names that kind of joke about fireman.
There is also lots of roads/entrnaces behind the scenes you don't normally notice.. and of course they can drive out into the paths if needed. Normally for EMTs, etc you wouldn't see them drive out there, but rather walk with stretchers, etc. But if needed, emergency vehicles can drive out there.