If you have your drive axle out, it is a great time to pull the chaincase completely out and check / replace the bearings and seals. If you are not going to do this, then some grease the bearing and some don't. Yamaha chose to leave the backside seal off so the bearing would actually seep a small amount of oil (somewhat filtered) from the chaincase for lubrication. I feel that it is most important to ensure that the seal and he O-ring in the collar is lubricated and I usually put a new bearing in which comes lubricated. If you cram the cavity full of grease the oiling effect will likely not occur, but I suppose this could be ok as long as you keep it greased.