You sound exactly like the dealers the Simplicity engineer was talking about.
The bearings are sealed.
Greasing the spindles does nothing to get grease into the bearings. The only benefit is to coat the steel against rusting (which it does not).
There is absolutely no benefit to pumping grease into the inside of a spindle. None. The bearings are sealed.
As far as water flowing upwards, its water vapor. Evaporation. Whether open or not makes no difference. The spindles are going to rust. But no grease will make its way into the sealed bearing. (Otherwise their not sealed).
What was the second line of my reply ?
Quality mowers have greasable spindles that last for thousands of hours
So old spindles where there are no grease nipples fitted go in with a light coating of grease on them to surpress rust which it actually does fairly well if the owner does not use the deck wash system.
New housings get grease nipples put in them and like Star the inner seals get pulled and where I have one that fits a metal shielded bearing ( Z ) goes in the top so I can keep the housing fully packed with grease and the air has somewhere to escape
These housings never ever come back for bearing replacement unless the owner runs the blades down till they become unbalanced or bends the blades with the same result.
There is only 2 reasons for fitting a 2rs in spindles
1) to cut costs while a plain & sealed bearings are the same price in bulk , you eliminate a complete step ( fitting the nipple ) , 3 machining events ( seals & nipple hole ) plus 3 parts ( 2 seals & a nipple ) and also save on grease .
2) EPA rules in California ( and some other states ) that prohibit grease nipples due to the chance of grease getting into the environment .
Just about every commercial mower comes with greasable spindle bearings.
And as for the service life of sealed bearings I would note that Great Dane who made probably one of the best ZTR ranges used a heavy 6300 series sealed bearings in their spindles and the routine service interval says to change them annually .
JD use an identical spindle housing with greasable bearings & grease seal ( you can swap them over ) but their spindle bearing replacement schedule is 5 years or sooner if required .
The landlord has 4 x 2000 series Cub Cadets ( all from the 90's) which he mows pasture , orchards , scrub around the creeks & the house yard with.
The paddock mowers go through around 3 sets of blades a year to give you an idea of the useage and 3 of these are still running the original tapered roller bearings