Keypad matrix questions


I'm working in an Arduino calculator, but I do have some questions about the setting of the keypad matrix. My first vision was this image:

This schematic is used in an easyPIC6 and I was wondering if I could use the same matrix in my project. The question is, this circuit would work with my Arduino Uno R3? Are the diodes really necessary? Because I don't think so.
Can the Arduino recognise if an OUTPUT pin has grounded or has connected?
If It does then I'll continue with the project, if It doesn't I'll need your help setting a matrix for a keypad 4x5.

The diodes prevent "shadow" key presses (if you press more than one key at once).

Use the Keypad.h, no resistors needed.