The composition of an antler is not the same throughout, the exterior portion is harder and more durable - if you cut straight through an antler, especially in thicker areas the "marrow" is more friable and more likely to degrade over time. As that is where the holes to secure the button would be, I would think not ideal to use as a button long-term and still retain it's function. If you look up antler "splits" for dogs you can see what that interior looks like - a bit spongey.
