Its not as simple as just saying Player X can't play in the NBA and can play in Europe so therefore European results mean jack. Its not an apples to apples comparison. There are elements of European basketball that are close or equal to NBA-level. For instance, the size-to-size ratio is pretty much equal. European bigs (at the highest levels) are just as big (maybe even bigger) than NBA bigs. But the athleticism between the average 6'10" NBA guy and 6'10" EL guy? No comparison.
Because of this, certain things translate better from Europe than other things. A penetrating guard, for example, is less likely to be able to succeed than a dominating rebounder and shot blocker. I think the things that Valanciunas does are more translate-able (lol) than the typical Euro prospect. I think the same thing about Kanter, too. Not so high on Vesely, though, as he seems to lack a few of the most important things it takes to succeed as an NBA wing (and he clearly isn't suited to be a real PF).
Still, its not an excuse to dismiss the Hoop Summit. It has proven in the past to be a very good tool for evaluating NBA talent. Both are very valid forms for evaluating, and I would struggle to put one above the other in terms of importance.