I have pretty much road with every cheap or high end hub there is. OK not every one of them. I have used my grease zerk trick for years now nary a problem. Sealed cartridge bearings are of coarse a little different but loose ball bearing hubs I do it to all of them. When you pack a hub good there will be a little grease seep out at the bearing seals but nothing out of hand that can't easily be reckoned with by one quick wipe over a couple of rides.
Heck I had bikes that I put grease zerks/certs on and some I never even covered the 1/8 hole. Never had any remorse from doing it and never a prob for me. I never had the grease come out of the 1/8 hole just saw it squirm out the bearing seals on my plain jane loose ball hubs. It's pretty nice to see the old black grease squirm out and the purty new grease show up.
Just think of how bearings buddies work on a Automotive trailer or boat trailer.
I got nice sealed cartridge bearings on the Boxer. Front wheel bearings never seam wear out on any of these bikes.