That was what I wanted to know, too. Ever since IAM launched, I've been wanting to authenticate ssh against it. Sadly, the docs all seem to specifically say EC2 instances running windows.
there is no mention of integrating with IAM but they do mention optional RADIUS support, which means you probably have to configure ssh yourself
I'm not able to spin up an instance to test with this week .. but if my linux hosts -inside- my network can auth to my corporate AD (and they can!) I don't know why an AWS EC2 instance would be different.