Marc Has it right. The only one of those skis that really have a revrese side cut is the ARG. It has really odd demensions. It has ruler straight edgest that go out from the tip to about where the toe piece is... so the ski gets wider from tip to center and then under the boot iit has the tiniest amount of side cut.... if i remember correctly its about 2mm on each side. this is so when your using the ski at a place like whistler and you need to get form whereever your skiing deep snow back to the lift the skis arent usless like say the spatula, a true reverse sidecut skis, would be. than the tail is the same as the tip. The ARGs are fairly stiff compared to the rest of the skis you mentioned. then im fairly certian they have flat under foot and big rocker in the tip and tail. Everything here is to improve Pow performance.
the hellbents are just a really wide traditionally shapped ski with a big rocker in the tip and tail the rocker helps with float in deep snow and it also i guess helps prevent hooking the tip and tail on the lip of a jump because the tip and tail are raised off the snow already so it helps to get everything out of the way. In general though people usually talk about the rocker helping with butters and float more than eliminationg hook.
The ep pro is similar to the hellbent in that it is traditional shapped with flat under foot and big rocker... the eppro however is much much softer and it also has the early tape you were talking about. think of this like stretching the tip out so that the widest point in the shovel is further back on the ski and it is less abrupt than in a normal ski. this is like marc says to reduce drag in pow and it does infact help to reduce that hooking of the tip and tail on lips of jumps because the contact point is so much less abrupt and there really isnt anything to hook.
The JP is another weird ski with a lot going on. the tip and tail have an early taper, so it has the sort of stretched out tip like the ep pro... but it almost looks like a stubby short ARG becuase what happens, is that the ski almost flares out at the contact/rocker point so that the tip and tail essentially have a mini reverse sidecut. You have to think about it lke three skis in one. a reverse sidecut ski at the tip, a traditional sidecut ski in the middle, and another reverse sidecutter in the tail. THEN armada put in what they call their "elf shoe" tech (yeah i know... kinda gay name} but that is rocker in the tip and tail for float and then rather than flat under foot, it has real traditional camber. This all makes for an axtremely versitile ski. But whats really cool is that armada found is that this shape is really conducive to park featers becuase the shape of the tip and tail elminated hooking because of the early taper and the rocker helps with butters, they took the shape of the JP, cut down a bit on the rocker and made it much thinner, and the alpha one was born. a really really awesome ski.
I hope that answeres all your questions.. all the companies are fooling around with a bunch of differnet things. I dont think though that everyone will be making ARG copies though ( i think that was your question at first). The ski has its place but it is very specialized and not too practical out of the deep snow.
