Like danemyer said, if the backer boards arent there, there isnt anything of any substance there to screw into. My last three fivers had the factory ladder set ups on them, and with my 250lb frame, I dont trust these to support me fully.
I use a super ladder to get me to the top wrungs of the factory ladder, then step on to the roof from there. The factory ladders scare me, as they are just bolted on with plastic hardware. And a fter being exposed to the elements for a few years those plastic stand offs are brittle.