It depends of the time of year. Breakfast at Kona Cafe rarely fills, and you likely will be able to get a table without a reservation. But during the busy holiday seasons and even during the free dining promotion, every restaurant becomes crowded, making your chances unpredictable.
If you have an idea of what day you would like to eat at Kona, I suggest making a reservation. There's no harm in having one, and you can easily cancel if your plans change. Otherwise, just wing it and see what happens.