So @ 30 I took Scion of the Ethereal and am wearing the L. Braided Cutcord. The Scion of Ethereal Display Icon isn't shown in my buff bar at the same time as the Silent Avenger Icon.
If I un-equip the Cutcord and lose the Silent Avenger set bonus the Scion Icon appears.
I have noticed that the Invisibility Guard procs even w/o the Scion Icon so I am hoping it *is* a display error and the other benefits Scion of Ethereal provides work as well.