Gratuities on Royal Caribbean are obligatory, so it is a matter of when you prefer to pay them.

This is not a gratuity then. You've misinterpreted the word. Gratuities are gifts not required payments. This is a fee that you pay. Instead of just tacking on random fees and whatnots why not just set the price of the cruise to be the price of the cruise where you can pay your employees or the wages that they expect. Because at the end of the day it's all coming from the customer's pocket and now you just look like a bunch of douchebags because you want to line item out a bunch of fees and call them gratuities when gratuities by their nature are optional.

If the service is bad, can you get your money back?

Is there any way to verify that gratuities are actually paid to the service workers and aren't just pocketed by the company?

If not, then this defeats the incentive and purpose of gratuities.