the only thing with hrew and pipe is it has a seam - most use dom becasue it is seamless - i personally have seen many cages done out of hrew and SOME out of pipe - i honestly must say that it is your life under the protection/ steel and i just see it fit to use the best material for the job - anyways it is possible but the fatugue is what will kill it - or that 3,4 or 5th roll over which must always be taken into consideration
there is a thread on pirate where the pipe bender is converted for tube - pretty cool i will see if i can find it