Right now, the lethality of this outbreak of Ebola is around 60%, so an infection is definitely not certain death, particularly with the supportive care possible in the U.S.'s best hospitals.

When you've already dedicated yourself by traveling across the world to help people fight a highly-contagious disease, it makes sense that you'd be first in line to test a serum (which, while experimental, uses a method that has had great success in the past).