Most boat trailers don't have brakes, so the excess grease that brearing buddies push past the inner seal doesn't contaminate the linings. Brg buddies prime function is to expell water from the brgs, and supply fresh grease before the brgs rust.
Some travel trailer axles have grease fittings , But those are set up to push the grease down the center of the spindle, to the inner bearing,then back through the outer brg. and the excess is wiped off the outer brg, that system doesn't blow any grease past the inner seal , and the fitting is covered by a rubber cap.
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.