In my honest opinion, NO.
1, it will not help protect from dents at all. Matter of fact, if your hull dents easy, it will make the epoxy peel off pretty quick.
2, there is alot of prep time, and you will have to put several coats of the stuff on there in order to make it last.
3, the epoxy can and will scratch, and once it does, its a matter of time before it starts to peel off.
4, yes it will help you slide some, it can and will cause your boat to slide right off the trailer and onto the boat ramp if you dont keep it hooked up all the way to the water.
In my opinion, it would be worth it if you put it on a slick bottom boat with no ribs, and it was a boat with a thicker bottom that was pretty dent resistant. It would cost alot of money, but it would work... Then again, If I had a slick bottom john boat, it would have a sheet of polymer on the bottom of it just like my airboat...
with you having ribs, the very slight benefit you may gain will not be worth the TIME AND MONEY it will take to get the stuff on there... JMHO....