True! Many of the early ambient pioneers came from or were inspired by the progressive and krautrock movements. Tangerine Dream and Brian Eno being two of the main crossover artists that started to transcend genres (Eno mainly after his coma).
When you hear an album like Ricochet from Tangerine Dream from 1975, about 3 years before Eno's Music for Airports, you can already hear the ambient undertones coming through:
(ofcourse before that there were already hints of this with Dark Side of the Moon and other progressive artists)
Tangerine Dream ...
back to the high school for some of us ...