The tips are not added to the cruise fare unless you get pre-paid gratuities, such as when you select My Time Dining. RCI has gone to automatic gratuities, but they are charged on a daily basis to your shipboard account.
Some are confused by this but these are two distinct methods for assessing the tips. Pre-paid cannot be removed since it was part of the cruise price. But for everyone who did not pre-pay, the line charges $12 per person/per day ($14.25 for suite guests) to the account. Those can be removed.
There are no vouchers provided anymore. The cabin attendant will leave some envelopes on the last day for those who wish to give a little extra in cash.
That offer you mention is a promo by an agency.