I just discovered that if the Query.ReturnIdsOnly property is set to True, then the ObjectIDs property of the FeatureSet of the result is populated, but the features themselves are not. If this property if False, then you get features but not the ObjectIDs. Weird.
I manually created a List(of Integer), looped through the FeatureSet and added the object ID's using feature.Attributes("OBJECTID"). Not my favorite approach but it worked.
Ted Chapin