So, it worked just fine. A few things to note...
If you want in/out privileges with Marriot, you have to register your car and it's a higher rate. If you're just paying it for the week, no need to register.
When you depart, they ask if you were on the cruise. If you say yes, they will yell at you for parking there and claim it's a higher rate. We had an error with our ticket and she had to manually ring us up. Cruise rate was $90 but the regular overnight at $13 would have been $91 for our sat-sun, so if you're staying the night before, it's a wash anyway. Easy walk to Port and we'd definitely do it again.