Interesting... if using appropriate materials and properly making the weld and protecting it then it should be a moot argument when the concrete is poured...but at least now I know.
Using the "proper material and method" only means it was done to the least highest standard. The "proper" steel gas line, is a very poor material to bury in the ground, but an inspector will approve the installation. I have had 1/2" lines silver soldered to a 2 x 1/2 tee, and the branch of the tee broke off because the fitting's "hardness"/temper had been destroyed by making the joint.