Yes, as long as a bar is displayed, the parameter is identified. Only when no bar is shown the parameter is not identified at all. Identification strength ranges from 0 to plus infinity. By using a log scale, the domain now is (-\infty, \infty). Values between 0 and 1 in terms of identification strength will therefore show up with log values that are negative. A 0 values in the level will be minus infinity in the graph, which is the reason no bar is displayed as you cannot plot infinity.