I read an interview with Dime before where he said he knew nothing about theory or the names of scales, he just worked it out what sounded good slowly then sped things up when he was happy with a particular lick.
Man, I don't know what the fuss about Dime is at all, I have to say Hammet is a better player in terms of musical expression. I do agree that Hammet went downhill in a big way in recent years though. Anybody who doubts his ability to shred should check out the Justice For All album... tracks like Shortest Straw and Blackened have amazing lead parts. Also his leads on the first three albums although not the most original were entirely memorable and had a definite groove (most of them anyway).
Dime was a great player but I think he went downhill too, especially over the last three Pantera albums. The leads on the Cowboys From Hell album were excellent and had style of their own but I think the band in general traded technical skill and musicality for groove and ease of playing in live situations after Vulger Display of Power (much the same with Metallica after Justice For All). If you have all of both bands albums, ask yourself this, what are each players two best leads... then compare them... Dime's were brilliant but I reckon Hammet still wins hands down.
Just my 2 cents