Most (all?) new boards have diodes, the only way to be sure is open it up and have a look. You will need them and if it doesn't have them you'll need to cut a trace going to each switch, which is not fun.
The Arduino Micro is a good choice if it has enough pins so depends how big the matrix is - a fullsize board probably won't fit. The 328 based Arduinos don't have USB support so avoid them.