Well that is quite incorrect. Most NITs and IIITs have a doctor who does some basic checkup for eye sight, color blindness, weight etc. But these doctors do not check your PwD status. In the JOSAA brochure there is a specific format given for PwD which has to be filled by a registered govt. doctor of any place. You come under PwD only if the doctor who is signing your form declares you as such.You have to produce this form at this of counselling and admission as proof.

All the best!