first the proof
ok now supposedly no one on the arr cbt forums has been able to get this working because it always gives an error or simply wont render over the game, I got it to work and im sharing my method here, if you want to repost this in the beta forums feel free but please give me credit :P I cant post there at the moment because of the stupid posting limits they put on the forums
First , open steam, go to add non steam game
Choose FFXIV not the system info one but the other one
open the properties on the shortcut after it gets added to steam and place in the following lines
Target = "C:\Program Files (x86)\SquareEnix\FINAL FANTASY XIV - A Realm Reborn (Beta Version)\boot\ffxivboot.exe"
start in = "C:\Program Files (x86)\SquareEnix\FINAL FANTASY XIV - A Realm Reborn (Beta Version)\boot\"
do this exactly and close it then restart steam, , you may have to do this several times for it to save.
run your game , you should now have steam overlay, enjoy
note, don't alt tab from the game, or the steam ui breaks and wont reappear