Cobearnicus has nailed it - the question of what the note 'A' is tuned to is surely irrelevant (unless, perhaps, your piece is a drone on A...)
What's interesting is how the notes are tuned to each other in the scale. Equal temperament has some rather audible problems with it. Since ambient music very rarely modulates from key to key, it seems sensible that this music should explore other tuning systems wherein intervals are more mathematically 'pure'.
(This wouldn't make sense in jazz, though, because in jazz you modulate from key to key a lot, very quickly. Same in classical music. This generally sounds bad in tuning systems other than equal temperament.)