There is currently relatively little work on architectures and evaluations of robots that support creative designs of human interactants in manipulation tasks through dialogue. We build a dialogue system by integrating a large language model into a robot cognitive architecture and investigate whether engaging in dialogues with the robot collaborator on a creative task has positive effects on task satisfaction and experience of the human, evaluating the effect of dialogue on perceived robot utility, intelligence, and supportiveness as a creative partner. We test our hypotheses with a cake decoration task during which participants collaborate with a robot arm equipped with a mixed-initiative co-creative dialogue system to place decorations on a dummy cake. The results show that the participants prefer robots that make reasonable suggestions compared to random suggestions and that they perceive those robots to provide more creative support.