Can I use marine plywood as a deck surface?
Marine plywood is not that different from CDX plywood they use the same glue and pre press process and hot press cure process. 

The main difference is in the veneer used , tight knots , with the core plugged so there are no voids compared to cdx.
 Even marine plywood needs to be protected from water so you will be adding a paint or other material on top , drilling holes for drainage creates places for water entry Into the core. It may sound like a good idea I would just about guarantee it won’t last as long as a dimensional lumber surface with a simple stain. Have you priced 5 quarter marine ply? I don’t think you would want a deck made out of anything thinner than 5/4 and that may be pushing it. If it freezes in your location don’t use it, the water will penetrate the wood and when it freezes it will come apart. 

Again the difference is in the quality of the veneer and by the time you go thick enough and seal it you would do better with a wood or composite product.