In principle yes, this will work.
I'd rather use woven glass though, or bi or triaxial UD, this will result in a much better fiber to volume ratio and will be stronger. The outermost layers can be made from mat to prevent print through.
If you can make the deck a little thicker then do it, every millimeter counts and will make the boat much stiffer and stronger since stiffness of a sandwich is proportional to the (thickness)³.

Post pictures of the boat and the damage.

Hi there. After some advice regarding a project I'm starting. I run a small offshore race boat of a catamaran design. Between the two hulls is a flat deck of around 1m wide by 2m in length. It was made of 10mm marine ply wrapped in a glass fibre mat and finished with gelcoat. It comprises of three panels.  This broke last year due to the impacts of the two passengers landing on it and the ravages of time. The deck does take a beating as it also has the fuel tank strapped to it. I'd like to replace the deck with some boards that have the same or better strength as the plywood but be as light as possible. I'm looking at using 10mm foam board with outer layers of glass fibre matting and a resin topcoat. Will this be suitable and as strong? Thanks very much. Any advice would be greatly appreciated. Steve.