How many do you think there were? And what do you think is a chance for a single park employee to die during a given summer? To me, this still doesn't make any sense whatsoever.

Maybe the ranger was talking about all the workers at the park? Looking at the NPS site, the park seems to have 9 hotels most with restaurants. So I'd guess there's probably maybe 1000 seasonal service workers in the park. 1 death out of 1000 seems plausible.