It doesn't specifically say, but on page 17 of the brochure on the website it says "Built strong enough to allow periodic maintenance on the roof" and it shows 3 people on the roof. It also says you have a ladder.
Given that I'd assume that you could walk around on it if you're careful. If you're concerned you could always use some thin paneling to help support your weight.
Salem 29RKSS Pushing a 2500 Mega-Cab CTD!
Gotta go campin!