SC2Mapster

You could give them a buff behaviour that searches for nearby units that applies a revealer to them.

If adding the event directly to the portrait actor does not work then set the portrait up to use Signal events and your Unit actor to send the signal to the ::PortraitGameSelf system reference. Else do like Vikings and send the event action directly to that reference.

https://www.sc2mapster.com/forums/development/data/162956-solved-can-we-change-portrait-per-unit