The term "awen" is documented in medieval Wales; Giraldus Cambrensis wrote about Welsh mediums called awenyddion, "people with awen." It's entirely possible that it has some kind of link with AUM via very old Indo-European roots. (I've documented chunks of unrecognized Indo-European myth in Iolo's writings, so this is at least plausible.)

On the other hand, I tend to think there's a lot to be said for the possibility that there's some essential reality of which the two words are not merely arbitrary reflections.

Still, this is fascinating. There are a number of other odd parallelisms between Japanese and Celtic (and proto-Celtic) traditions -- Japan, for example, has quite a few burial mounds and standing stones that look remarkably like those in Britain and Ireland.