It seems crazy that robotic troops can suffer stun and especially bleeding, but I don't see anything in the rules to say they can't. Am I missing something, or should I simply imagine that it's some other effect (jammed motivator, pierced fuel pipe, or something)?

See this post:

http://community.fantasyflightgames.com/index.php?/topic/133370-probe-droids/

Spanks Fizz