I wouldn't walk on it. A dark boat is a magnet for scratches and cracks in the gel coat. Even if the glass itself doesn't crack, the gel coat, on a multi-color boat, can get pretty thick. Gel coat doesn't have any reinforcing fibers and is very brittle. You will see minor cracks in the gel coat in the high-stress areas, like in the corners of the dash.
Lastly, if you allow people to walk on the deck, that is an open invitation for people to stack coolers and $#!+ all over it while scuffing their sandy feet across it.
If you see it flexing like that, it could be a "light layup" or the glass could be degrading on inside. Try to climb in there and see what is the cause.
Welcome by the way,
Joe