CafePress has the same stipulation as Zazzle. They mean that you cannot take someone else's photo or design and put it up as your own where it could become a liability. If a model is licensed for a commercial render and you use it in that render, then you are fine. Might not be a bad idea to put in small letters the credit for 3DCafe though. Photographic subjects, like models used in renders, also can have restrictions on what can be used in a photo commercially. Most subjects that can't are certain commercial buildings/landmarks. logos, people, etc. Always best to check first.