I don't see much utility in a reel that you cannot get wet. I do submerge mine on occasions, either accidentally or intentionally, and I have yet to have a reel fail on me, in 20,000+ hours of flyfishing.

Well, there was that time I dunked the reel when it was below freezing, and took off the spool to shake the water out so it would not freeze, and the drag ring came flying off and vanished in the river, but someone found it later that day and I got it back!

Good idea to keep them lubricated and clean them periodically. Also, putting a reel down in sand or dust is a good way to get them full of stuff.