I think thats a good question. Page 9 even shows a stat card for the Commander with traits. To bad the rulebook did not address those traits. Looking thru the faq, I also did not find anything to clarify the issue. But a forum search did bring up a thread that stated those commander traits are immunities. I don't know how accurate it is though.
Too bad the rulebook does address that on page 32, under bosses.
It's a decent sized rulebook and all of it needs to be read.