All sharpening stones are whetstones. To "whet" is to sharpen. There are several different families of whetstones, the two most common are oil stones and water stones. I think, that by "wetstones" you're referring to water stones. The Edge Pro company doesn't sell oil stones for its sharpeners; and I can't think of anyone who sells oil stones cut to fit the EP.
Edge Pro sells polish tapes and water stones for its sharpeners. Other water stones and oil stones are available from a few retailers. The Edge Pro sharpening stones are really pretty good, but some of the after market stones are better than the Edge Pro stuff -- but not hugely. Put another way, either way you'll get a sharp knife but the other stones do more to improve the [cough] "sharpening experience" by making it go faster and leaving a slightly finer edge. Upgrading the stones falls into the category of not really necessary, but worth the extra money.
However, as far as I know, stones cut to fit an Edge Pro won't fit in any other sharpener -- except perhaps the CanadaKnives counterfeit which was around for a few years on ebay. I just don't know about that one. So check the labels on your sharpener before buying anything.
If you do own an Edge Pro, I suggest either buying the Bester 500, Beston 1200 and Suehiro Rika from Chef Knives To Go, or the Chosera 400, 1000, and 3000 from the same store. The first set will sharpen as well as the second, but require a little more forethought to use because the Bester (which you'll hardly ever use) and Beston (which you'll always use) require a few minutes of soaking before use.
In addition to the stones, you'll need to buy a flattener which you'll need to use BEFORE using the stones, this one is the best deal I've seen for flatteners.
As you use and flatten them your stones will wear unevenly, and if you're very picky about sharpening angles you'll also need the angle cube and drill stop collar. But you're probably at least a year away before you need them. Maybe next Hanukkah.
I have a lot of sharpening stuff, including four different kits. One of those is an Edge Pro Apex using all Chosera stones; and in my full size, water stone kit the two coarsest stones are the Bester 500 and Beston 1200; and even though I don't own one, I know the Suehiro Rika very well. All, highly recommended.