The 3D Analyst toolbar tools are not always enabled when a LAS dataset is active. This is because the LAS dataset can be displayed as a point set. Analysis on thinned points is turned off, and the tools will only be enabled when the LAS dataset is displayed as a full resolution triangulated surface. To learn more about how to obtain a full resolution triangulated surface see: LAS dataset scalability.
However, the tools are not always active when working with LAS datasets and the 3D Analyst toolbar tools. The 3D Analyst toolbar tools are only available when a LAS dataset is displayed as a full resolution triangulated surface. A full resolution surface is indicated in the table of contents when 100% of points are being used to construct the triangulated surface. When the LAS dataset is displayed as a point set the tools will be disabled. To learn more about how to obtain a full resolution triangulated surface see: LAS dataset scalability.