Yes, the Byakugan is known for its insight. It's ability to see the flow of chakra is the greatest amongst the three Great Dojutsu.
Because it can see not only the color and collection of chakra in the brain (where Genjutsu is supposed to target), but it is also apparently capable of detecting the color. As mentioned by xxSAGExx, Ao used it to see that Mifune was manipulated and that Danzo was the perpetrator. Furthermore, he was capable of detecting that the chakra color Danzo used was different.
And this was done by a Non-Hyuga. If we compare that with the Sharingan via Kakashi vs Itachi, it would be likely that the actual blood line users can use the ability even better.
I would also mention that Kakashi turned to Hinata to see if Genjutsu was being used on the group during the Itachi Pursuit Arc. Having already thought the same thing, Hinata replies that she had already checked and confirmed it wasn't Genjutsu.
So yes, the Byakugan can see and detect genjutsu.
