I don't see a lot of hazard in that arrangement. There is not a lot of spring in the wrenches, chain, or union, if anything breaks it is just going to go slack and fall to the ground. Keep toes out from under.
I work with pipe wrenches like that and it is always done with cheater pipes, you notice the longer wrenches do not have the swell/knob at the end of the handle like the shorter ones do, it is that way for a reason. 2 guys with cheater pipes, a lot more can go wrong involving them smacking each other in the face, than that come along keeping human flesh out of range.