You need your feed dogs engaged for a walking foot to work. The purpose is to feed the top fabric evenly with the bottom. Lowering the feed dogs means that the machine doesn't feed any fabric through, top or bottom, so the walking foot would be useless.
The best foot for lowered feed dogs is probably a darning foot of some sort. I'm sure there are more people with a lot more expertise on the FMQ end of things. I've done a lot of free-motion embroidery and I'm pretty sure the process is very similar.