The durometer on most knifegrinding contact wheels is too soft for this application. The rubber is going to cup slightly at the edge of the steel. You will not get as precision a surface as with stone wheels, even with a harder rubber, but except for critical applications it won't matter. It's a lot faster than stones, too, especially in applications like flattening damascus billets. The first one I'd ever heard of was a chap from Michigan back in the 80's who'd made one that was engineered so well he could put near a mirror finish on balisong blade flats, his specialty. Wish I could remember his name, but that was more than 2 minutes ago I last remembered it.
Can anyone help me with the name? He sorta hung with Chuck Stewart and the Gottages in the 80's.
Many of the folks building their own conversion have happily purchased wheels from Bertie Rietveld in South Africa. He sells a higher-durometer wheel:
http://www.batavia.co.za/