That is very interesting - the 3 hun and 7 po go back to China, as they are discussed in early Daoist texts. I didn't realize that part of the imagery had survived in Japan as well, though I guess I shouldn't be surprised.
Is the usage of hun as being equivalent to yi/intent common in Japan? I've never come across that before. Though I haven't looked very hard.
No, it's no common, and I could well be wrong - I based that on inferred meaning based on the passage quoted and a number of other places.
As you've probably already figured, Ueshiba loved rich imagery, encoded text, and multiple layers of meaning in a single phrase. He'd also phrase the same concepts in various different fashions in an attempt, I suppose to get what he was talking about across (it's like this - or maybe it's more like this...).