To be fair, Busch Gardens Tampa goes all out and decks out their ENTIRE park with lights (and BGT is HUGE if you've never been) and they do it with a crew of less than 10 people. My dad used to do it and then would start before Howl-O-Scream even started and do the work overnight. On top of the lights, they had a huge (and expanded last year) snow area where you could not only build and play with snow, but ride down "snowy hills" in snow tubes.
Now understand that they had no light show as impressive as Osborne. They did have a few, but they weren't too impressive.
So yes, it is possible to do a park-wide event, especially in such a small park like DHS, but the overall guest satisfaction would be lower and the quality of the event likely wouldn't be much higher, if at all.