You don't need evidence of an abnormal life cycle (which would take a funded project just following the animals around) to prove that the feeding is harmful to the animals.
The immediate effects on the animals are obvious, you just have to look with your own two eyes. On the very skin of the issue (pardon the pun), the sharks have skin discolorations around their mouths. These are sores caused by the little boats hitting them while they feed. You can also see yellow, green, and blue boat paints rubbed on the skin of the animals.
On another level, the shrimp they are feeding the sharks are OVERFISHED. They ran out of shrimp locally, so they're buying dead shrimp from other provinces, some about 11 hours away. Nobody knows what would happen if you feed iced, dead, decaying shrimp to a whole colony of Whale Sharks. Would you really take that risk? Can you also imagine what would happen if a whole level of the eco system just vanished just to sustain this feeding program?
Finally, the sharks are getting used to boats. The boats in Oslob don't have propellers, sure. But these sharks have been trained that boats = food, so after feeding, these sharks go to places where boats HAVE propellers and this is what can happen :
This is Fermin, one of the first few sharks to be fed in Oslob.
Just don't do it.