myVEGAS has added Carnival Cruise Line as a Partner.
Carnival Cruise Rewards are limited to 3 per player in a 90 day rolling period (similar to the MGM Rewards 3 in 30 Days limitation, but this is 3 in 90). They are also limited to one Reward per sailing (which makes sense, since they are only offering cruises, not add-ons).
The Rewards are good for one room with 2 people. Rewards must be booked within 14 days (the cruise itself can be much further in the future – right now, dates through July 2018 are available)