Cooking through Chris Lilly's Big Bob Gibson BBQ book, you will notice the man seems to have a thing for soy sauce. It makes its appearance in marinades, as seasonings for his steak, and in his signature red barbecue sauce. In very few contexts does it use soy sauce as an "Asian" flavoring. He explains that Alabama's been incorporating soy sauce into their beef dishes for the past half century.
This is particularly interesting as soy sauce is not a subtle flavor yet it has been blended as an ingredient in such a way by Lilly that it doesn't overpower his dishes with an Asian accent. Not that there's anything wrong with that, but the art is incorporating foreign ingredients and making it a uniquely American seasoning.
Salt Lick Barbecue in Texas also incorporates soy sauce as part of their signature mustard sauce. This is largely due to a Japanese matriarch of the joint and it's 100% Texan. Cuban cuisine as well as Peruvian cooks have long added soy sauce as part of their flavor profiles.
Soy sauce was developed in around 2 BC in China and became actively traded all around the world by the late 1700's. We see various types of soy sauce being used all over Asia. Japan alone has over 10 major varieties of the stuff. For the most part you can break soy sauce down into 2 major categories - DARK and LIGHT.
DARK = Sweeter, thicker, and likely to stain your meats a dark color. Better for glazes. Best not to use in injections because it stains the meat. Even for marinades, be careful how much you use.
LIGHT = Saltier, thinner, and possess more of a soy "flavoring" better or marinades, injections, and seasoning.
The big reason you can blend soy sauce into BBQ is because it's a fermented product like Worcestershire. The process develops Glutamic acids which enhances meaty flavors. My personal favorite are the mushroom flavored soy sauce for that double punch of umamai.
I believe this is an exciting trend where more and more people in the US will begin to use soy sauce in manners that are different than how they would be used in Asia. When one thinks of Alabama BBQ you lean more towards the seasonings that are part of the general South eastern american landscape like brown sugar, ketchup etc. But now we can confidently say that soy sauce has a firm place in the barbecue profiles and it has nothing to do with Kung Pao Chicken.