Right now the CDC guidelines allow a passenger to be treated as vaccinated if Pfizer and Moderna are mixed, but not AZ. This is something that is changing literally day-by-day, though, so it’ll probably be different by the time Disney sails (assuming vaccination status matters for sailing on Disney at all).
For non-US sailings that care about vaccination status on other cruise lines I’m seeing that generally mixing Pfizer/Moderna with AZ is allowed, but some cruise lines are only allowing it if AZ is the first dose.