I myself have had a zillion wheel bearings apart and repacked, replaced and all that. It's not a hard job at all but, does take at least some minor equipment, fluids (cleaning) etc. to do the job correctly. When I do it, the bearings are thoroughly cleaned and blown clear of any left over old grease and whatnot.
Then while I do have a repacking attachment for my grease gun, it's a whole lot easier to just grab a glob of grease, put it in my left palm and, with my right hand, start working that into the cleaned bearing. Takes about a minute to thoroughly pack a bearing.
Now, as for all dollies having repackable wheel bearings, well, I'm by far no expert but, there have been on here, reports of some that are SEALED bearings. And even many of our Jeep front wheel bearings are sealed and non-repackable. So, for you dolly towers out there, I'd definitely yank a wheel off and do whatever's needed to find out WHICH version of bearings you have.
If you're not the type that does your own work, then get whomever you choose and rely on, to do the checking and or work for you. Oh, and to the OP, not that it's all that important but, you might get a moderator to change your title. "Grade" your wheel bearings", hmmmm. Yeah, we know what you mean but, it's just a slip.
2004 ITASCA HORIZON 36GD, 2011 GMC Sierra 1500 4x4 Toad '18 Honda Africa Twin Adventure Sports DCT
Retired-29.5 yrs, SDFD, Ham - KI6OND
Me, Karla and the Heidi character, (mini Schnauzer)!