Cornsnakes are rodent specialists, even in the wild. While there may be the occasional opportunistic feeder foraging a birnest, they are not egg-eaters by nature, and as such, are not equipped to eat and digest whole eggs.
On the other hand...I feed my Florida kings cornsnake slugs when they are laid, and they seem to LOVE them...BUT snake eggs are VERY different than chicken and bird eggs in that the shell is soft and leathery, and able to be punctured by a kings teeth, where a bird egg would seem a tough challenge to even the most persistent king, IMO...