THAT looks like an old borer hole the tree filled in to heal it over. I'm working right now on a black locust bow with one of those smack in the middle of the belly. On mine, the tree had sealed over the hole well with two heartwood rings, but the belly has that exact puckered slit, with that exact grain pattern. Funny enough the hole was closed in with wood like yours, but the wood was still white like sapwood right around the slit, maybe 3/8" on each side.
So, I lucked out that mine is on the belly. I just worked around it like I would have a knot.. I injected the slit full of Minwax wood hardener, then gently pounded a tiny shaved splint in the splint with lots of glue.
On the BACK, like you have, is a different deal. If.you trust the grain , I guess go around like a knot, but the grain looks squirrely around the ends of that slit. If those were simple checks I wouldn't think twice. AND it IS osage. Will a binder hold it? Do you need.to go down a ring? I'm curious. Good luck!