I would wrap that area with something like fast flight serving, fishing spider wire etc. The soak down with super glue. Rawhide wrap could also be used.
Sapwood is part of using a limb, sucker, sapling for a stave. Cracks, checks are also common stuff to deal with.
In 1990 Sonny Inman from Ohio let me shoot one of his limb bows and I was hooked! I've built, shot, mine and others, and hunted, killed with sapling bows!
And no you don't need overlays on locust bows!