If I have to remove and disassemble a spindle, believe me it is getting new bearings. Pretty cheap insurance.
At one time the bearings were coming with cheap grease, that is long gone and if you use electric motor grade bearings, those have pretty good lube spec.
No need to pop the seal etc. (actually most folks tweak the seals and they just don't seal as good as when new), grease is important but keeping out water and dust is upmost. I have not seen a mower deck bearing fail because of the grease but many are contamination related. String, twine, and mono-filament are mostly what I seen takes out the seal and bang bearing is filled with dirt.
I have been running sealed bearing in mower decks for several years and no issues. Think about it, the mule drive bearings are sealed and some i have are 40 years young.
If your deck needs bearings and you have issues with getting down to service them.....go with sealed bearings. they will run along time.