We had the DDP one time while staying at AKL. We ate at Boma often (and have gone back several times on other trips) and we've never had an ADR. The most we've ever had to wait was about 30 minutes, and that's the same time for a regular restaurant around town here on a weekend.
I think that we've never experienced a long wait there because it's a buffet and there are no characters, so people are eating and leaving, not having to wait for the characters to make their rounds.
We were just there in January, supposedly a slow month, and the walkups at BOMA were waiting over an hour for a table. The lobby area was jammed with people. We were glad we had our ADR's.
I would definitely make an ADR as Boma is a very popular spot any time of year. For our trip last June, I called every day for 2 months before our trip(and also once in Disney) with no luck at all for dinner.