As far as i know, the first (if not only) priority is to use the wiimote only for head tracking, so accelerometer would be useless - unless you want to wear the wiimote on your head :P
Since the wiimote will only be used as a camera, you'll probably be able to use it with any currently supported FT setups (1, 3, 4 LEDs).
The point of using it isn't to have a wii-like control on your PC, but to have fast head tracking - the wiimote does all image processing required to locate each point on the captured image and calculate its coordinates (the process that right now takes most CPU time used by freetrack) all by itself , and then sends coordinates of up to 4 points it sees to the FT. From now on, getting actual head position its a matter of simple calculations (easy for a computer to calculate, not easy to program
). That's how the TrackIR works by the way - all image processing is done by hardware.
If you want to use the wiimote as you would on a wii, search for software called GlovePIE - it supports its accelerometers, and probably the sensor bar as well, and is extremely configurable - it's a kind of scripting language, you could actually write a freetrack-like head tracking in it using the wiimote.