Wagx2-If you have a bearing with rubber seals(2rs) they're not greaseable within a housing, they are sealed. If they are metal shields(zz type) they are greaseable within a housing capable of such. The metal shields are permeable to allow the grease in/out.
rubber shields were removed (small pick to get under the edge they pop right off, really not much holding them on) from insides of the bearings before they were installed, so the grease could go in/out within the housing,and housings id. was enlarged to allow grease direct path to bearings sort of like gear oil in rear end, as grease heats up it will be allowed be thrown around the inside of the housing. figured they weren't designed for the added friction the weight will add, and that they would get hot, designing the housing to allow extra grease and surface area for it to get rid of the heat was only way to go, maybe over kill, but think it will work. if I would have used metal shielded bearing would have need axle seals, and both housing would have had to be 3/4-1'' wider.
so you can use either bearing, but one will need a separate seal, guess its preference, at that point when building.
pick up a used rs bearing the next time you change one(not one bearing so bad it eat the seal) screw driver will take right off, but new bearing use a pick with a fine point catch outer edge and pry up it is removable, buy all my bearings with rs option, then decided if its used. and removing one side doesn't mean you have to remove both seals is not part of the race so doesn't effect operation of the bearing.
learned this rebuilding a Honda, tore it down took all bearings out, went down to local Honda shop, to replace all was 260 some odd dollars, so I kindly said not right now,

and there was a allied bearings, dealer just a block from the Honda dealer

, stopped by there, he took numbers off the bearings and seals, went to the back grabbed all but I think 3, which he had to order. I looked at them

then told him "hey these are sealed, there not right motor oil has to go thru them" he grabbed small flat head, popped off the seal said " remove them if you don't need them, want hurt a thing" he rang up all the bearings, and seals and 3 that were ordered. ---- $58 bucks and change. roughly 200 dollars in savings compared to Honda dealer. been using Allied Bearings ever since, only been a hand-full of times he couldn't get the exact bearing or seal that I needed. motor been running ever since, and I been a Phil Robertson, happy, happy, happy!!! Customer of theirs, every time.
and if you don't bugger them up when removing, you can put it back by pushing rubber lip back into rim of bearing, there not really a sealed bearing water and dirt seeps in that's what wears them out to start with.