Should I be concerned about the 3 conduit nuts that are way down inside my UDS?
I don't believe so. It doesn't get hot enough at the bottom air intakes (That's where I assume they are at.) to create a situation where galvanize will offgas. Even if it does, I don't see where the ppm will get anywhere near what would be required to make you sick. The nuts I used are the same as yours and I have countless cooks on it and no one has gotten sick.