In my opinion, the key is to use a finish that is not slick when wet, and that can take the bumps and dents that a paddle must absorb.  An epoxy finish would score poorly on both measures, I suspect.  I use Valspar Val-Oil, an oil-based sealer that penetrates the wood fairly well and dries -- slowly -- to a fairly hard but not slick finish.  Some people use tung oil with a bit of japan dryer added.  I'm sure there are other, similar finishes; the key is to protect the wood while leaving it resiliant and enabling you to get a good grip on the shaft but still be able to slide your hands along it.

Personally, I've never bothered to finish any of my paddles.  I find I like the feel of the wood better without it, and I don't have slipperiness issues to worry about.  I have never "worn out" a paddle before it broke anyway, so I don't worry about it at all.

If I get to the point where the wood is "aged" more than I like, I'll retire a paddle and hang it on the wall.  Until then, they get used and probably abused.  I don't worry too much about that though, because it only takes a day or two to build a new one and they're very inexpensive.

FrankP