Base layers can only be displayed in 3D View as a texture on a surface. This is because a base layer typically does not have any inherent 3D attributes. Point cloud maps and point cloud layers are not surfaces, they are instead a collection of points. Therefore, there is no surface for the base layer to be mapped onto.
If you wanted to display a base layer on LiDAR data, you could grid the LAS or LAZ file, generate a contour or color relief map, then click Map Tools | View | 3D View. Details on how to do this are in the following knowledge base article: I create a profile through my point cloud, but I don't see anything. Why?
Updated September 19, 2017