That email response sure would be interesting, richoso...
I think most of our methods for prep/cooking of meats are based on traditions passed down through the generations. Some of these traditions were long ago based on theories regarding cross-contamination and safe cooking temperatures, etc, while other methods are based upon proven fact through modern science.
As for using the same container for different types of meats for a marinade, and especially simultaneously marinating two (or more) types...I can't say that I would ever use that method...I can say that the idea just doesn't give me a very warm, happy feeling inside. If I knew this method was used for a meal being prepared for me to eat, I would likely be skeptical about partaking. Would my personal convictions on the subject be justifiable? Until proven otherwise to me, in what I would determine to be an acceptable method of testing, yes. So, that said, I would lean towards the "traditional" method of not mixing meats before cooking...ever. That's just me...
A contradiction to my statement about not mixing different types of meats is a common practice, which I do enjoy eating regularly...beef/pork mixed country style sausage (smoked or fresh), purchased from a meat market back in my childhood stomping grounds. There are many other sausage/wurst recipes which contain two or more species of meats, including among the most common, which there is a high consumer demand for...I speak of none other than the good ol' hot dog, which is, as any of us who read labels knows, loaded with stuff that most of us would rather not ingest.
My opinion is this: when in doubt, don't do it. In this case, how much more trouble would it be to use two containers for marinating the meats separately? Not much...maybe an extra 20 seconds of clean-up time...so, why risk raising someone eyebrows over it??? I try not do anything when I prep or cook which may cause someone else distress...if I knew someone didn't trust me to cook their meal...well, that wouldn't make me feel very good..not one bit.
I digressed...again! LOL!!!
Eric