Not really. Pulling the cap or bearing buddy can reveal if there is water in there but only on the outer bearing side.Is there any full proof way to check the bearings et cetera before you experience a fail on the highway? Jack it up, wiggle the wheel sort of thing. Or do you need to pull it apart ever so often?
For some reason they’ve never made any advancements in axle bearing technology as there isn’t anything for the inner bearing with the exception of the dexter axle passageway and that isn’t very effective either.
A compromised greased bearing will last quite a while as long as it has grease on it. But you pretty much gotta inspect them yearly or you’re putting yourself at risk imo