Nope.
Cecil H. Green was an Englishman who spent some time in Canada before moving to the US. Eugene McDermott and J. Erik Jonsson were both born in the US; I can't find much on McDermott's ethnic background (but I'd guess Scottish or Irish), but Jonsson's parents were Swedish immigrants.
By the way, due to their philanthropic and political work (Jonsson was the Mayor of Dallas for a while, and he helped greenlight DFW Airport), their names are all over Dallas. There's a major arterial in the suburbs (McDermott Road), the main branch of the Dallas Public Library (J. Erik Jonsson Central Library), a bridge named after Eugene McDermott's wife (the Margaret McDermott Bridge; she was a philanthropist in her own right) etc. And of course half the buildings at UTD were named after the founders.
One of the early donors to UTD, though, was of German descent: Karl Hoblitzelle. He was born in the US, but he was ethnically German, and both his parents had German surnames (I don't know if his parents were born here or if they were immigrants). Like the other three, his name is all over the place here: I first heard of him because of Hoblitzelle Hall at UTD, and there's also a Hoblitzelle Park in Plano, plus plaques dedicated to him all over Downtown Dallas, and probably more I can't remember. He founded the Majestic Theatre, which is the only part of Dallas's historic Theatre Row that hasn't been bulldozed in favor of office buildings (and it's still a functional theatre!).