I get on my roof at least two times a year. I recovered it a couple of years ago (rubber roof) and I get up there with a tube of EPDM rubber once a year just to goo any places that look like they might need it. The biggest thing on a rubber roof is wear tennis shoes and don't twist your feet when you walk up there. To turn pick your feet up. It is possible to tear, separate, or otherwise damage the roof. If you're careful it's not likely.
I'm 6'2, 235 and it's no problem. I walk very gently and stay to the sides as much as possible.
If you're checking the condition of the roof look closely around the edges where the rubber is pulled over the sides. That's where cracks will form and water can seep in under the rubber and down the sides, inside of the walls. You gotta look close to find these types of cracks sometimes as you can't necessarily stand there and see them.
Also, depending on the construction method, check the rear corners rear good. It never hurts to put a little EPDM rubber caulk down on a spot that looks questionable. Just don't use anything else on a rubber roof. Unfortunately, EPDM caulk can't be found at Lowes, Home Depot, etc.. You'll have to get that at Camper World or similar place.