Of course, why wouldn't emulators and most games allow you to change the keys. No need for a symlock.

The keypad should work just fine as a controller, the only downside is that without a d-pad and with only using thumbs, you can't really walk diagonally by pressing two keys at once, at least not to the upper left and upper right (unless the game uses some clever control scheme which splits up horizontal from vertical movements to each side of the keypad).

For most emulated platformers or RPGs it should be no issue at all. Custom games will come up with smart control schemes, probably involving the accelerometer in most cases. And if you need more, you will certainly be able to connect external controllers in various ways.