My 2002 Crestliner has a Heritage custom trailer and probably the company that rebranded with the Crestliner name to match the boat. I had never seen anything like what I saw at the end of the axle for a water proofing device. I always used after market Bearing Buddies on previous boat trailers...once I happened on them many years prior.
I apparently have the ez-lube axled (don't know if its the same brand/system that Ranger Boats uses on their trailers) and it has an aluminum cap that covers the workings....easily pries off with a screwdriver. Adding grease via zerk forces the spring loaded plunger out where it's length is visible (from the side) with the cap installed. i connect the grease gun and start pumping, watching the plunger extend as I pump. When it quits I quit and replace the cap. Having had the rig for going on 3 years now, I have had to add grease once.
As time and usage progresses, I can see the cap slowly move toward the axle and when it gets close enough, I add grease. I'm of the opinion that these are OEM parts that have not been replaced over the years and here it is 19 years later and when I periodically jack up the axle and spin the wheel....during winter storage, it still rolls and rolls and rolls free as a bird.