This site is being deprecated.
Please see the official X‑Plane Support page for help.
Yes, the tool Ortho4XP supports the creation of custom orthophoto base meshes based on a multitude of online image providers and raster DEM data in either .hgt or .tiff format (as readily available on viewfinderpanoramas.org). A support thread is available here.
IMO this is BY FAR the easiest method to create custom meshes for X-Plane.
Converting .bil files to either .tiff or .hgt should not be rocket science (Google is your friend).
This site is no longer being actively maintained.