Can ps3 use a keyboard?

May be...

Any conventional USB keyboard is compatible with PS3. Although I recommend the official keypad because it fits right on your controller without adding much weight, has every key possible that you'll find on a standard keyboard, plus it has a useful touch pad that you can use in internet browsing.

Yes, any normal usb keyboard works great. I use one. You can use a usb mouse too. You can even play Unreal Tournament 3 with a keyboard and mouse, if you think it's superior.

Yea Logitech has a wireless one for bout $80 bucks and there's probably a Keypad for the controllers

Yes