Well I think I salvaged it. I took the granola mixture and put it in a bowl and added some water, put it back on the sheet and scored it. I am thinking that you either need to use wet spent grain or else add water. Dried grain, 3 eggs, peanut butter, and flour didn't create enough of a paste to bond the treats together. After baking it for 30 minutes at 350 with some water introduced, it bonded better. It was a little crumbly breaking up the scored pieces after it was done baking, but it seems like this was normal.
For future reference, do spent grain recipes usually call for wet grain, or dried grain? It looks like some people freeze the wet grain while others dry it by baking it overnight at a low temperature, which is what I did.
This really *isn't* rocket science, but between last night's first attempt at brewing all grain and today's attempt at dog treats it seems like the process always has plenty of room for error and improvement.