Yep, that's been a heated topic of discussion over the years...birds dripping onto other meats below them, or even other birds...drippings are drippings...doesn't matter what it came from...if it's potentially hazardous food such as birds, fish, beef or pork, it's still drippings from cooking flesh. The only concern I would have is if a bird (or meat) just dripped a bunch of raw juices onto something I'm pulling out a few seconds later...maybe just a peek to look at drippings a few minutes before you remove the lower meats and compare to what you see when you actually want to remove it would be prudent, or even rotate the stuff you're going to pull to a higher grate position 5 or 10 minutes before you removed it, as an extra measure of caution in the event that there are nearly continuous drippings falling, would be more than adequate. Surface temps of the meat those drippings fall onto while in the smoker makes for a very short-lived risk of illness.
It just don't matter! Lets say you cook the Chicken for 2 hour, then add the Raw Hens because they only take 1 hour. The Hens are just GUSHING Bacteria laden juices all over your Chicken or Ribs, Brisket, anything in the Smoker. From what you have read you think, " OH MY GOD I AM GONNA DIE! " WRONG!!!!
Those juices are dripping on " 225+°F " Meat! Just how long do you think the Bacteria has to live!?! Seconds? Let's say they are Super Bugs...A Minute or Two? It just don't matter what you put on top of what, the heat will kill it...JJ
That's the common conclusion and not a big deal with many smokers...BUT...If you have any of the Bullet type smokers, WSM, ECB, or an Ugly Drum Smoker. You have to take the whole thing apart to load the birds losing all your heat and smoke. Not to mention the big blast of O2 that hits the fire you just spend 3 hours tweaking vents to get to that perfect temp and the risk of burns and dropping the first bird. All a waste of time because it just don't matter who is on top of whom...JJ
I'm new here and have no experience, so please keep that in mind, when I ask this question.
Why not just reverse the pecking order (pun intended). Put larger cooking bird on top and add smaller, quicker cooking birds underneath.
Seems like you could time it so both came out about the same time fully cooked, and safety concerns would be moot.