I know this thread is ancient, but maybe someone else stumbles upon it following the same bread crumbs.
As far as I can tell, bAllowConcurrentTick is for Component Actors only.
For Actors the property would be PrimaryActorTick.bRunOnAnyThread = true (it is false by default).
After enabling it in a test, my average CPU usage doubled with noticeably more cores working.
I don’t know if it is available for Blueprint actors, but exposing this would be a no brainer (e.g. create C++ actor class add the line to its constructor and parent BP actor off of it).