The Marriott Rewards Program has been combined with the SPG Program to become one program. You can get all the details of the combined Marriott/SPG Program here.
Members of Marriott Rewards can earn points, elite night credits, and receive elite benefits at The Ritz-Carlton. The Ritz-Carlton Rewards members will be able to earn points, elite night credits and receive elite benefits at all Marriott hotels. However, members may only have a primary relationship with only one program at a time. That is when staying at a Marriott or Ritz, you can only earn points and elite night credits in one program not both. It is possible to change membership from one program to the other by contacting Guest Services.
Also note, that the terms and conditions to both programs are the same. The programs only differ in the promotions that the members of a given program receive. This being the case, it may make sense if you are married to have you and your spouse belong to each program. That is, one of you belong to Marriott, and the other belong to Ritz. I am going to switch my account to Ritz Carlton now and leave Rob in Marriott. 🙂