Do you need a keyboard to play? No. The game is solo-friendly enough that extensive communication is not required. In dungeons he will be able to get by with basic commands, many of which are in the auto-translate function.
But to enjoy the game to the fullest he will want to communicate extensive (it is an MMO, after all). In practice, it is impractical to type in a linkshell, free company, etc. all while trying to level or whatever. So although it isn't required I highly recommend a keyboard.
Any USB keyboard should do the trick. I got mine off Amazon for less than $15, shipping included, and it works without any problems.
You might want to consider picking up a USB extension cable to, if your PS3 is far away from your seat.