Hi low n' slow,
are beta probes used in the same way there are alpha probes (as seen on some fighters?)
I've never seen any such probes on A320s.
The FCOM simply says the FACs modify the sideslip indication slightly to show the pilot how much rudder to use ... (ailerons & spoilers retracted).
We used to do the same on 707s - simply apply rudder until you don't need any aileron, and bank slightly into the live engines to maintain heading.
As gum's would say - done by feel - didn't need a Beta target.