Lets do math, 7018 welding rod: the "70" stands for 70,000psi tensile strength of the weld if done correctly (obviously we are all pro welders, also dont worry about the 18). estimate the surface area that you have welded on rectangles are LxW, just treaty every surface that the weld covers as a rectangle and add up the surface areas. say you had 4in^2 of surface area. 70,000=F/4, F=70000*4, F=210,000lbs. so if you had a weld that covered 4in^2 it would take 210,000 lbs to break it (straight pulling it). lets say a jeep weighs 3500 lbs, give the weld a safety factor of 12 for shock load 12*3500= 42000lbs so for straight pulling you have a design safety factor of 6. bending is a little different but still due able. not saying you should not do it through the bumper, just a interesting way of looking at it.
commence hating.