To the best of my knowledge, there have been ZERO suits of Angel Flight
pilots with regard to any mission flown.

Given some of the frivilous lawsuits that are filed in the US every
day, well... you can pretty much sue anyone for anything. Doesn't mean
you are going to win. At some point you just have to make a judgement
call about how you want to live your life. A doctor refusing to stop
and render aid for fear he might be sued??? Maybe he SHOULD be sued...
for not helping when he could.