One of my close friends was a student of NITIE Mumbai. According to her, the admission process of NITIE has two steps.
Like most colleges, NITIE follows a decent distribution of the marks. The distribution is - Entrance Exam(in percentage), Group Discussion/Personal Interview, Under-Graduate Exam(in percentage), 12th Exam(in percentage), 10th Exam(in percentage) and Work Experience(If any).
Although these factors are responsible, nobody can tell how particularly these factors affect admission. But in the interview, the student would be asked for the reason for attaining fewer grades in graduation. Therefore, the student should be prepared for that in advance with a logical and sensible answer.
In the placements, the shortlisting procedure is very unpredictable and therefore it's very difficult to say whether or not the grades will affect the shortlisting process. But the fact is that the NITIE has 100% placements and hence a student need not worry about the placements.