I would probably make one just in case, but you may not actually need it. The year before last we had such a fantastic dinner at Boma (and we had missed our arrival night ADR at another restaurant so we had table service credits to burn) that we stopped at the podium on our way out and asked about a breakfast reservation later that week, they were able to accommodate us easily. I think that most people who have breakfast at the resorts are either grabbing a quick counter service meal or they are lingering at the resort for the day (possibly checking out and traveling home). Not too many people want to waste their precious park time at a resort restaurant for breakfast or lunch.
I haven't been to the other two restaurants for breakfast, but we do breakfast at Boma once or twice per trip and it has never been very crowded or hard to get an ADR. It is quite a bit larger than Kona Cafe (not sure about Olivia's - I've never seen it).