I guess all I can say is, I know 300 refinishers who would disagree
. Sealcoat is found in most hardware stores. All it does for plywood is slow the absorption rate for stain (one could also use 'sizing' which is nothing more than watered down Elmers glue. If you have ever stained a soft wood or a highly featured one... the stain does not go in evenly.... it can look blotchy and muddy. ...'sealing' the pores allows a more consistent absorption.
My advice would be to get two test boards.... treat one with sealcoat cut 50%... then make test strips of your possible;le color stains (or dyes).
You will convince yourself....who is... the most important guy in this project!
Test strips allow a mistake not to happen.