If they haven't been pulled, inspected and repacked for 4 years, definitely go for that option. Brakes should be inspected and serviced too.
I think people give the "EZ Lube" (Dexter's name, lots of copies out there)axles more credit than they deserve. You can't just grab a grease gun and run around your trailer pumping grease into the bearings. There is a specific procedure and it requires jacking the trailer wheel off of the ground and rotating it while greasing. This allows the grease to distribute evenly and also helps to prevent overpressurizing the inner grease seal and getting grease into the brakes.
Also, The EZ Lube feature is not intended to replace regular bearing maintenance. From the Dexter FAQ section of their website:
E-Z LUBE - What is the E-Z Lube option?The E-Z Lube option was designed specifically for the marine application where the axles are constantly being immersed in water. This feature provides a convenient method for purging the water from the hub cavity without having to pull the hub every time. The hubs should be removed every 12 months or 12,000 miles to inspect the bearings and it is imperative to replace the seal at this time to assure that the grease does not leak out the back onto the brake linings rendering the brakes non-functional.
Jim & JoAnne
2016 Toyota Tundra SR5 TRD Double Cab
2004 Starcraft 11RT (Replaced by)
2011 Eclipse Milan 18CK Travel Trailer