No he's not, when u run SLI u only can feed 1 monitor.
When he switch SLI off he can feed 4.
And it has nothing to do with how much ram u have.
And u say the OS use the "invisible" ram when it needs it, is
When u have an 32-bit OS, u can install 4GB, but windows 32-bit can only adress 4GB memory total.
Thats incl your video ram on your videocards.
So with his dual GTX cards, he will only see (and use) ~2,75GB in windows.