I read something online saying when painting OSB you needed to scuff it up a little to remove the light wax coating some of it has and apply a good primer compatible with your main coat. That and seal the cut ends very well with multiple coats soaked in.

That being said, the only experience I've ever had is painting over some older OSB shooting houses that were already degraded. Seemed to work OK for the couple years after that I was still in the club. It does soak up paint as you can imagine. I used a very coarse napped roller to make sure it got down in all the crevices.