Can I get admission into NITIE in the SCM or Ops course by taking the GATE mechanical? If yes, what is the cut-off?

Yes, it is possible to join NITIE by any of the GATE examinations streams. Few of my friends got admission at NITIE through GATE. 

Admission to NITIE Mumbai through the GATE examinations from any stream of engineering will make you land up at NITIE in PGDIE – PG Diploma in Industrial Engineering.

There are two new courses available at NITIE, Mumbai: PGDPM – Project Management and PGDMM – Manufacturing Management. You can take admission to these courses through GATE too.

Coming to cut-offs, it varies from year to year. For this year the GATE cutoff score (general) was 609. If you feel you have a decent score and you'll get a GD, PI shortlist, and then you can convert it.