How does AIIMS Delhi treat a student who has cleared the AIIMS entrance exam on the 3rd attempt?

Honestly speaking there is no distinction between those who cleared the AIIMS entrance exam on the 1st attempt or 3rd attempt. AIIMS Delhi just admits around 350 students over the period of 5 years leading to a family-like bond among all students. No one is outcasted or made to feel inferior just because of the number of attempts they took to clear the entrance. What matters is that eventually, you managed to get into AIIMS Delhi which in itself is a great feat. 

It's better you discard such negative thoughts and focus on your studies with positivity.