Hi there!!!
Yes, Shastra University gives admission on basis of Board marks , basically there are two types of streams through which you can enter in Shastra University for B.tech
Stream 1 : Through jee mains
As you are not going to give jee mains so I am directly explaining the admission procedure on basis of Board Marks...
Stream 2: Through Board Marks
This is done by normalising the 12th boards score of the student and there are 30% seats  through this stream.
As you asked that  will you get  a seat by scoring  percentage more than 90%  in board exams , than I must say there are high chances of getting a seat however the competition is very high...
Hope you got your answer,Do upvote the answer if it helped you...