I've been very busy at work lately, and haven't had time to touch my Galileos or my Edison at all for several weeks. 8-(
I think trying to quantify what does and doesn't work is a good path to go down. I also think there are a couple of different problems here, which may be muddying the waters and making git harder to see the patterns.
Problem 1) USB devices do not show up. I'm not sure whats going on with this. IIRC, there was something about not booting your board with USB devices attached or else bad things can happen. I don't remember the detail or the result, but hopefully someone else will. I have used a UVC Webcam on a Gen 1 board and do not remember any particular problem with it. I don't think I have trued using a USB hub myself.
Problem 2) Modules complain about missing symbols. This sounds like some kind of data corruption. I am unclear on whether or not the system boots to a prompt or now when this happen (I suspect is should, but would be lacking networking, USB based ttys etc.). The one things I have suggested here is to run "update-initramfs -u -k all" once you do get to a prompt. I don't think I seen any replies here of anyone doing this and whether or not it made a difference.
Is there a 3rd symptom that does not falling either one of the above? I thought there might be, but ATM, I cannot remember what it is.