Warrior Dash is fun but not a physical challenge of strength but more one of cardio endurance.
If you hit the gym on a regular basis and can run 3 - 4 miles you will be ok.
Best to run in a group and go through the obstacles rather than run around them. (You are paying for them) Your likely to face running / walking in water, mud, on sand, up dirt hills and go over various balance challenges and go through a climbing wall or two.
Have fun and enjoy.