Quote Originally Posted by Archangel
Exactly, probably because if it was in constant use it would be impossible for him to maintain that eye, the same as kakashi
Except Kakashi's Sharingan is always in constant use. That's why he covers it up. This would seem to be the case with Danzo.

It's probably because you can only see the chakra while using the mind contol technique. So Danzo would probably just not use it around people with Byakugan.
That's assuming quite a lot. Also Ao sees the chakra in Danzo's right arm as well as his eye, so it's got nothing to do with the sharingan at all. The image shown is the same one we see that every Byakugan user sees. To my knowledge the Byakugan can't tell what kind of jutsu is being performed, and Ao simply recognizes Shisui's chakra. He never actually says "Danzo is controlling everyone."