Yeah, I suck at counting. I meant to say 12 likely outs, but accidentally double-counted the Jack of Clubs. Even if he has only 10 outs given Hero's set though, it's still a plus EV play:
http://twodimes.net/h/?z=882225
pokenum -h ad ah - qc tc -- ks 9c 5c as
Holdem Hi: 44 enumerated boards containing As Ks 9c 5c
cards win %win lose %lose tie %tie EV
Ad Ah 34 77.27 10 22.73 0 0.00 0.773
Qc Tc 10 22.73 34 77.27 0 0.00 0.227
This is almost the worst case scenerio, and he is still getting enough (barely) to make this call. It's close, but not definitely wrong.