Schlick's approximation and GGX are orthogonal concepts.
Furthermore, it's usage so far has been inconsistent: we don't even use it with anisotropic SchlickGGX, and Burley (Disney) diffuse does use it while its name doesn't indicate it.
The use of Schlick's approximation in Burley and GGX is an implementation detail and doesn't need to be reflected to the namig.