THe SID foot has a small piece extending underneath the center - it is sort of like a plough that runs in the ditch. I'm not sure why you couldn't use it. However, the purpose of the walking foot is to keep the layers moving at the same speed and you won't (or shouldn't) have shifting between the top and the backing.
I agree with the others that it is not necessary to do SID stitching before FMQ. Just make sure you do a good job putting the sandwich together (nice and taut) and baste well.