if a student belongs to sc category and scores exactly the qualifying cutoff percentile in jee mains, then yes he can get seat in nit or iiit based on jee mains rank, sc category cutoff for nit usually around percentile forty to forty five, and iiit may have similar or slight lower requirement, after jee mains results counselling is done by joints e seat allocation authority jesaa for nit iiit and gfti seats, the student enters jee mains roll number category and round by round seats are allotted based on rank choice and category reservation, if qualified percentile matches the cutoff and seats are available in preferred choice then allotment happens, student must complete document verification pay fees and join college within given timeline, for exact cutoff percentiles and previous year data please check full details here

https://engineering.careers360.com/articles/jee-main-cutoff-trends