Obviously it's something that CAN be done, but the question is..... Will you create more problems for yourself then you solve?
-"Rock" wheels abrade away as they are used, constantly reducing the diameter. This means the wheel is constantly reducing in size....changing the way it grinds.
-They come in very limited grit sizes (this means you have to figure out other methods to "clean up" the grinds)
-Compared to abrasive belts the amount of stock removal is painfully slow
-"Rock" wheels "glaze" and/or clog more so then abrasive belts, and are more difficult to clean/deglaze.
-They are very sensitive to speed versus how efficiently they work.
-The are susceptible to chipping/breaking
-Compared to abrasive belts they are just plain more dangerous to use.
I don't mean to be the rain on the parade, but I simply can't see any advantages to using a "rock" wheel for blade grinder over a belt. I guess that MAYBE, if an individual doesn't own a belt grinder, and only wants to "play" with making a single blade, it might be more economical, but if it's something a person wants to try, in order to see if knifemaking is for them....it's just gona drive you away.