I tried merging 2 actors. There are problems. There does not seem to be a way to make 1 the "master". Suppose you have "Gwenyth Paltrow" with pictures and info, etc and "G Paltrow" with just a movie credit. If you merge the 2 you can get "G Paltrow" surviving and all the info from "Gwenyth Paltrow" missing.
I tried merging 3 different actors. After the merge all were gone and the movies had the actor deleted from the actor list.
When you merge actors (say 2 actors next to each other in the "A's"). After the merge the cursor flies to random parts of the list instead of staying on the merged actor. So every time you merge you have to go back to the spot on the list and continue. Very annoying if you have hundreds of actors.