Levity,
It depends on if the grease is on the outside of the wheel or the inside. If on the outside, the bearings were probably overfilled and if you have a bearing buddy type of outer cover they are designed to release the excess grease through a vent hole. If the grease is on the inside of the wheel, then you have blown the rear seal and this will require some attention soon. I recently had this happen to my trailer with brakes. If the rear seal blows and gets grease on the brakes, then you will need new brakes.