Well, why not? Having a designer doesn't mean you can't make decisions yourself, sometimes it merely galvanizes an idea you have and more often than not, opens the door to an overall look that you knew you wanted but didn't quite know how to get there from here.
Also, with FDG, you don't always have to spend a lot of money and have a designer on board for the duration of your project. One of our specialties is coming in and spending a couple of hours fine-tuning what is already present, or adding that legitimacy to what has already been done.
In the end, hiring a designer can only enhance the final product whether the entire concept is worked out or simply being able to add clarity to an otherwise tenuous direction.