As far as I know, we have never had a problem getting breakfast at Boma. Now we made a special trip to eat there since we like it so much and then planned to spend the bulk of our day at the AK park.
Now you didn't mention where you are staying. If you are staying at the Lodge, then I suggest that you go a little later. We had and ADR for 10 am and found the place to be only half full. If you have to travel there and don't have to use the busses, I suggest you plan to leave at least 30 to 45 minutes ahead of time in order to get there on time for your ADR. Granted we were there in Feb. but it was during Mardi Gras and the parks were a little brisk while we were there. I think that Boma's draw is more for dinner than breakfast but we thoroughly enjoy breakfast there.
Oh dont forget to order the breakfast "frunch" drink. We absolutely love it!
If you have any more specific questions please feel free to ask.