Last time I asked, steel target NOT attached to a frame of some sort are not permitted on the standard range at MCFG, so the walkers would be out. There is some question of whether the pistol walker may be useable in the bays, though; I did not ask that specifically so I would defer to one of the officers to be sure.
Steel (on the main range and bays) must be hung directly in front of a berm such that a bullet striking the target is deflected downward.