I'll agree with with Ken and say i too have spoken with a few american breeders who have created many of the new morphs out there .... and many of them use ambient heat for everything that is not being bred.
By this i mean, hatchlings to sub-adults, only when they are planned to breed do they go into gradient heated cages...
Can this be done with all snakes? probably not, some are more sensitive then others.
but some? sure. theres tons of proof.
Ken never stated he breeds them using just ambient temps...and quite frankly, i dont agree that "breeding" a snake holds any more weight then just "keeping" a snake healthy and long lived as a measure of success.
but i do agree that its essential for most species to have a gradient if they are to bred.
Grant van Gameren