Its usage is pretty close to fascist usage of Judaism, ca. 1930s.
It lacks a clear definition, but can comfortably include any so-called subversive element.
As soon as you have to limit your definition (Frankfurt school, or whatever), the term becomes academic and thus of marginal interest.
But then one couldn't use it to label things one doesn't like as "anti-Christian", or whatever.
The interesting thing cultural-Marxism-as-label is it's totally ethnically detached, or indeed detached from any non-verbal markers.
Anyone can be a cultural Marxist, if sufficiently advanced sophistries are deployed.