What About Linking Against OpenGL ES, or Vulkan, respectively?

It is not necessary to link against them. Both are loaded with dynamic library loading (except for iOS).

DynamicGLES takes care of it by dynamically linking OpenGL ES.

PVRVk loads Vulkan function pointers the optimal way, using per-device function pointers. These are stored into per-instance and per-device function pointer tables. Static linking is unnecessary.