So when the call WAS put through where does that leave them Pumpkin? It was pre-recorded and vetted BEFORE going out on the airwaves.
That's where I think it becomes the radio station's responsibility for airing it. I suspect they would not have done so had any information of a deeply personal nature been disclosed, but given that the ward nurse revealed little more than a series of stock medical cliches about the woman's condition, they went ahead with the broadcast. Like most broadcast organisations, they wanted to make some money, raise their profile, generate publicity - they're hardly alone in that, and their methods in doing so were hardly unique.
The prank was reprehensible, ill-conceived and juvenile, like the majority of pranks and stitch ups usually are, whether they're aired on a radio station or executed in between friends in every day situations. If there was any likelihood that prank calls were likely to result in suicide, schaudenfreude would never have taken off.
Say your best man ties your drunken fiance to a lamp-post outside a pub on his stag night for a "laugh", and then an out of control car mounts the pavement and hits him, fatally wounding him. Is it the best man's fault the fiance is dead, since if he had not been tied to the lamp-post he'd have had a better chance of getting out the way in time?
Tragic though the consequences were, I don't see that these two particular DJs are any more culpable or disgusting than any other DJ (or indeed human being) who either gets enjoyment from pranking, or seeing/hearing about someone being pranked. And I think we've ALL laughed at someone else's misfortune or embarrassment at some time or another.