JDE is all ready looking for Vertex. The integration with Vertex is all on the JDE side of things. Vertex doesn't have any "knowledge" of JDE.
B0000182.h contains all the vertex definitions and JDE vertex wrapper definitions. When a JDE session is created the tools layer actually calls some BSFNs as part of the boot strap process of creating a JDE user session. If you debug B0000182 and you have vertex installed (you may have to have it installed locally and have OCM mappings configured for your user ID for this to work), you will see that the function jdeInitEnvBSFN gets called simply by logging on to JDE. This function will initialize Vertex and store connection info and vertex API function pointers in jdeCache to be used by other BSFNs that need to make vertex api calls.
So bascially if you have vertex installed and configured as your tax calculator in JDE.
Logging in calls jdeInitEnvBSFN (B0000182) which establishes a vertex connection and stores connection info, function ptrs, etc. in jdeCache.
If you, for example, enter a sales order, functions in X00TAX are called that retrieve the vertex connection info from this cache record and make the required vertex api calls to calc tax, or do Geocode stuff, etc.