You don’t need to be literate to see pictures, which are kinda required for the more hands-on martial art manuals.
Admittedly it would cause issues with stuff like Ninjutsu or The Book of Five Rings. Especially the latter, which can be summed up as “read this, then read everything you can get your hands on, learn some actual physical trade like farming or smithing, and don’t forget reading everything you can get your hands on”.