Yes, jeans are allowed.

 But it is always better to wear trousers. NEET is an important exam, you should not take any risk by wearing something that might not be allowed in the examination hall. NEET 2018 dress code clearly explains the things you can and cannot wear on the exam day. 

For Female,

• Female candidates can wear light half sleeve clothes which should not have brooch / badge, big buttons, flowers etc. with trouser / Salwar.
• Candidates with Slippers or Sandals having low heels are only allowed and female contenders with shoes are not allowed to enter the exam hall or for writing the exam paper.
• Female Muslim applicants can wear traditional dress like Hijab / Burqa. However, those candidates wearing traditional dress have to come in the prescribed time before the commencement of test for undergoing the checking process.

It is said that, female applicants are requested to not wear ring, pendants, necklace, nose ring, earrings, or any kind of jewelry as those jewelry have to be checked before entering in to the exam center or hall.

All the best !