dear aspirant, hope you are doing well. here are some information regarding mop up round in NEET for students:-

Candidates who have qualified the exam can participate in this counselling irrespective of their domicile.
Candidates have to fill up fresh forms to apply for it.
This gives a better chance to claim a government seat irrespective of your lower marks than actual state cutoff.

so there is no rule that a student that has filled compartment exam can't fill the mop up round.

hope this will help.

for further queries related to this topic,feel free to post down in the comment section below.