Yes, that is correct. Any/All mods you wish to use will need to be in the same folder.
In your case, I don't believe it will matter which eq2ui_skininfo.xml file you keep (whether it's from the action bar or heroic bar addon). I've taken a peek at the eq2ui_skininfo.xml I have in my UI and I don't see any coding that directly calls on any of the other files.
DISCLAIMER: I am not a programmer, so I could be wrong ( it has been known to happen........once or twice
)