I spent 1 summer working in Yellowstone recently. My experience is that it's easy to move to a different position once you get hired. I had a crew of 9 people. 1 of the more capable employees moved from food service over to maintenance. Later he told me he was much happier doing that sort of work.
People are always leaving for some reason out there. turnover is somewhat high. They need over 3,000 seasonal hires to run the different locations in the park. If you didn't mind doing some grunt work until you got adjusted and then found something you'd like better, it may be worth it for you.
I was in a salaried position last time there. If I go back it will be as an hourly employee. I'd rather work 40 hour and have time off to enjoy the park instead of working 55 hour weeks. I'm not working for the money at this point. I take the job so I can park in their campground all summer long.
YMMV