No GST is not applicable for May, 2016 exams because GST can be implemented latest only by 01.04.2016. In that case, it shall be applicable with effect from May, 2017 exams. Good luck :)
Highly unlikely, as the Bill is yet to get passed in the Rajya Sabha and next by 50% of states in India. We all are put into wait and watch mode by the Parliamentarians, stay tuned for more updates and developments as and when events occur.