While there is cross-over between greco and freestyle, it is only one way. Greco guys can learn a bit of freestyle and possibly even hold their own just a little bit against freestylers. But my impression is that freestylers get owned in greco competition.
Furthermore even if there is a bit of "carry-over" between sports, champion Greco guys will never come over to freestyle and be able to compete on the same level or vice versa.
Here in Corea, you can tell who the greco guys are and who the freestyle guys are just by looking at their builds. The greco guys are built like fucking tanks. I think this speaks to differentiation in training from an early age.
I would agree with the original poster's comments about the value of folkstyle wrestling for MMA. Folkstyle has an exponentially greater emphasis on groundwork than freestyle and greco put together. The focus on riding, pinning and control translate well into a MMA format, as opposed to freestyle's rewards for cheap tilts and rolls.
I think that the difference in success between the two disciplines doesn't with the differences in the two wrestling styles per se. Rather, I think that it all boils down to boxing. Freestylers are often able to get away with not learning how to strike (Mark Coleman) by simply blasting people with long-range takedowns.
Since Greco requires the clinch for takedowns, I feel that Greco guys strike into the clinch much better, and hence learn how to mix up their wrestling with their striking much better than your standard freestyle champ.
Any "pure" wrestler from any discipline (greco, freestyle, or folk) cannot compete at the top levels of MMA no matter how accomplished they are in wrestling.
Great observations by Burton about the nature of greco vs. other styles (upright versus lower stance).
fos