1) The L/R2 buttons are mapped to the top two corners of the active touch screen; L/R3 are bottom corners. By default, the active touch screen is set to the front touch panel for all inputs. This is dictated by Main Menu -> Settings -> Input -> Prefer Front Touch. On = Front touch panel, Off = Back touch panel. So, if you set it accordingly; yes, you can use grips fine. Be warned; this cannot be mixed 'n matched (I.E. Front is L/R2, back is L/R3), nor can touch virtual buttons be mapped to hotkeys.
2) For the sake of simplicity, it only works with other Vitas (I THINK both host and guests need to be using the same architecture, I.E. ARM/x86, etc...). The XMB frontend's separate "Netplay Tab" is iffy at best; you're better off connecting via Main Menu -> Netplay.
--------------------- MERGED ---------------------------
If I'm to guess how this works, it's less you're giving special permissions to the folder for it to be unhidden, than it is you're actually taking away special permissions that dictate its system folder status; you effectively are turning the folder from a system-created one (hidden by "safe homebrew") into a user-created one (readable/writable by "safe homebrew"). And since all the system wants is a plain valid directory called "pspemu", it makes no difference to the pspemu/Adrenaline; hence why it works.