Dear Venkatesh, it depends on when the Supplementary exams are. The rule is that you should have completed your 10+2 atleast by the time of admission. So lets say the supplementary exams are in April/May and the results will be announced before KCET counselling starts, then your friend is eligible for KCET. However, if the exams are later and your friend cannot clesr his supplementary exams before counselling begins, then it serves him no purpose even in appearing for KCET because he will not be considered eligible for counselling.