there is no need to do anything. Grease may help a bit but can also be washed out. Also, ballbearings should not be overgreased.
Most of the cases I have seen are due to riding on the beach and parking the bike where it's rained on. Riding in the rain is not a problem.
good bearings are always better than cheap bearings but the rubber seals can't resist the pollutant (carbonic acid in rain and puddle water and grit). Once attacked, their working temperature increases, they degrade within a few months and need replacing.
I cannot say that anything like that has happened on either of my two e-bikes, or any of the normal bikes I have had over the last 65 years +, or most of the cars that I have had, many, but not all, who also have sealed bearings, often two per wheel, depending upon the design used.
My first e-bike I bought secondhand, I was told by the seller it was about a year old, I rode it for 6 years and gave it away with the original battery, carefully looked after by myself, with little or no loss of range noticed, but not tested for either...
All the motor parts were never "touched" by me as it just ran and ran, and if I remember correctly, somewhere about 18,000 Kms ridden.....In all weathers, and it was parked outside with just a cover over it....How many Kilometers it had been ridden in the first year, I do not have a clue!
What type of bearing also no idea!!
And even when I was in the RN, repairing both AC and DC motors, even quite large ones, with plenty of salt water and sea air, I have never had any such experiences.
They must all have had seals that were completely unaffected by such pollutants.....
But quality DOES play a significant role of course as it always does!
I personally also have not used or seen bearings that I could lubricate, except in my new bike's headset, and most bike's axles, the others were all lubricated and sealed for life, except for some cars wheel bearings, which were tapered and needed to be set to a specific torque on assembly.
You may find this informative:-
You must live close to something which pollutes the atmosphere where you live if that happens, and although I myself have never seen ball bearings with rubber seals, as they were always metal or some type of plastic.
Now I know enough to make sure that bearings with rubber seals are never bought, as it would appear that they are generally the cheapest bearing type available after checking up on the web....
Always something new and interesting to learn!
Thanks!
Andy