But, I don't think that there is a specific style of kickboxing that is characteristic of the Netherlands. And even if there is, I don't think that it is the result of some sort of fusion of karate or boxing or muay thai, or because that was the background of the first trainers in Holland. I'm not sure if that's what you're saying but I have heard people say things like that before.
First of all, if you look at muay thai fighters from Thailand, and probably Japan too, (and maybe even fighters from other stand up sports) you can find the so called "Dutch style" around well before the Dutch had even started doing muay thai. It would make a certain amount of sense if there were similarities between the way Japanese fighters fought and the way fighters from the Netherlands did, since the some of the same people who trained many of Japan's early muay thai fighters also trained many of the Netherland's earliest muay thai fighters and trainers.
Second, I don't see as much continuity of style in fighters from the Netherlands as some people do, if you look at the history. I think that Dutch fighters from the 70's and 80's especially, and even 90's, fight quite a bit differently from the way more modern fighters do. It doesn't really look like the so called "Dutch style" that everyone associates the Netherlands with.