Seems kind of redundant to me when spider rigging. The main purpose of the bobber is to control the depth you wish to fish. It also tells when you have a bite. When spider rigging you use long sensitive rods with enough weight to keep the line straight down and tight. You control the depth by how much line you let out and bites are detected by a twitch or bend in the rod.
Seems to me a bobber would just be in the way and would cause a drag on the line as you move along.
Just my two cents, I am not expert by any means.