1. Some companies include Gratuity (4.86% of basic) monthly in the CTC, however I would not advice you to do this as CTC is a cost to company and gratuity is only payable if an employee stays with the company for 5 continuous years so how can we show a cost to company when it is payable only after 5 years? That too with a condition and an assumption that employee will stay with the company. If you still are including it in the CTC what will happen to the funds you have collected from the employee if the leave in 4.5 years? They have all the right to ask it back since it is a deduction from the CTC and CTC was agreed in the employee contract.
2. No, why would an employee want to opt out? It is a big benefit plus a statutory payment given to an employee all they have to do is give 5 years of continuous service.