Is cross cutting good for cutting the top of ply wood?

No, it is not...it causes "tear out" or splintering. There are, however, numerous methods for avoiding this problem, or at least keeping tear out to a minimum. One can score the plywood first by setting the height of the blade just deep enough to score the top veneer, then recut all the way through. One can use a backer-board and set the saw blade deep enough to cut into said backer-board. One can also use tape. It works similarly to the above-mentioned backer-board to prevent tear out. Of course, there are others, but these three just came to mind. In fact, I used the backer-board method several times just today (I am a carpenter :).