Yes, you can definitely give the NEET exam after completing a diploma in engineering! There are no restrictions on educational background for appearing in NEET. NEET eligibility is based on your schooling, not your diploma.

You must have passed the qualifying examination (10+2) from a recognized board with Physics, Chemistry, and Biology (or Biotechnology) as core subjects. There is no minimum marks requirement for the qualifying exam, but securing a good percentage in these subjects is crucial for scoring well in NEET.

https://medicine.careers360.com/download/ebooks/how-prepare-for-neet-with-class-12-board-exam

I hope it helps!