No, in fact the owner's manual shows proper placement of the jack under the axle tube, just inboard of the u-bolt plate. I don't think you are supposed to jack up the back end with a jack under the pumpkin, but it has been done numerous times w/o any problem.
Thanks guys! I use my Hi Jack by putting the lift portion in the tow hitch, but can't keep it there along cuz balance gets thrown off. Got some jack stands, so I'll be doing using that for stability.