Involving your custom home builder and the architect early in a custom home project and making them work together is the best approach. Whenever you interview them, you can initially interview them separately and analyze their skills individually. But once you have identified a builder and an architect after the initial screening process, it is better to have collaborative discussion just to check if they can work together without any reservations. A custom home development project is a collaborative project and you need to hire professionals who work well as a team.
Never make the mistake of not involving your builder during the design phase of the project. I have seen projects where the architect or the designer works on the designs and the floor plans. In some cases, the builder would be completely out of the picture and would come in only at a later stage when the architect has completely finished. This is not a recommended approach for a custom home project. Such an approach may work for a production home but certainly not for a custom home.