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It will be interesting to see the responses here. I have definitely cooked them in the same cooker at about 250*. Just for different lengths of time. Brisket usually about 10-12 hours, ribs 5-6 hours.
I also like to lay my ribs flat. I don't know that they cook any better, but I feel like they do and they're easier to baste that way.
I've cooked, ribs, brisket, chicken, and pork all in the same cooker....just get your timing right, adjust for temp variations as you add/subtract meat and you should be good to go!