Can't say for sure. Here's the logic I use:
1. There is a wall between the Byakugan user (BU) and the Sharingan User (SU). BU looks through the wall at the SU's eyes. Does he fall into a genjutsu?
2. BU looks through the back of SU's head to see his eyes. Does BU get caught in a genjutsu?
3. SU closes his eyes, BU see them using X ray vision. Does BU get caught in a genjutsu?
If you say yes to any of the above, then BU will get caught in a genjutsu even with his eyes closed.
