They didn’t even mention the ninjas
He wouldn’t have believed them anyway: they have no proof, and another loyal general as well as the current Wataro heir told them about the Senshin plot (even though they were lying, Atsumori has no reason to doubt the word of his allies at this point).
Worth a shot. Plus he DOES seem to not be a scumbag, which is saying something.
Sooo…. naked and with an arrow protruding from your shoulder? Got it.