isaac, i am not the best person to answer you but im pretty sure you dont have to flash your kernel (i didnt) just to use it. just install the sixaxis support for n900, write your n900's blutooth address on the dualshock 3, then sync them.

i just got it working myself today, i didnt do any flashing or access to sudo. (although the system told me that installing the sixaxis will update the system)

as far as compatibility, im sure nokia will always build on the current firmware to release a future firmware, and with linux, this will easily be fixable IF there be problems.