That is a question you will have to answer. Have you had any trouble with the existing system. I assume yours is the kind that you pump all the grease out from the back. I always had good success with that system.
I have heard of old school people switching from oil hubs to grease but you are probably the first switching the other way.
Mine has the original "Cool Hubs" and they have worked reasonably well. Have changed seals a couple of times but never had any bad bearings with this system. The oil in the sight glass turns milky frequently and I have learned to just live with it. The bearings have never shown any wear or pitting and Ranger maintains that it only takes a couple of drops of moisture to make it look milky and does not hurt operation. I just make sure to replace it every year and go fishing.
People have had problems with trailer bearings with every system there is. An annual tear down and inspection will usually go a long way to keep it on the road trouble free. The only one I have seen that seems trouble prone is the Tie Down engineering hubs that Ranger and some other manufacturers were using around 2006 or so. But again, those don't just loose their bearings for no reason.
You sound a lot like me in that you like to have the best new idea you can on your rig. I have had the idea for a couple of years that I would like to change my sprung tandem axle setup for Torsion axles but I have not been able to get anyone to take me seriously. Seems like a bolt on solution for all the creaking and banging my trailer does while trying to back it up or turning in tight places.
I own a 97 trailer and was thinking the same, change to oil bath some time ago but due to this site reading a lot of the guys having troubles with them I stayed with the ones I got . But also reading as to where the guys with oil bath are changing to the Vortex hubs and so did Ranger .
Why would you want to switch them out to oil bath is my question. I can't see any real advantage to this. I would repack and replace any worn parts every couple of years depending on how many miles you pull the boat. The biggest thing is stay away from bearing buddies, or at least the USE of them. No need to ever shoot grease into a sealed system. All that this does is blows out the rear seals creating problems.
There is nothing wrong with with what you have. They have been using that on boats for years and years without issue. But, I'm also old school.