Serebii says it can (with Ditto as Arzamo pointed out), but otherwise I personally don't know.http://www.smogon.com/forums/showthread.php?t=39234
This will show which HP combinations, natures, and IVs of Heatran are legal. (or any other unbreedable legendary, for that matter)
Anyways, my question:
Can Phione breed to make more Phiones.