Our VMware team has been consistent in stating the Horizon desktop license can be used for virtual desktops and all infrastructure that support the environment (e.g. PSC/VCSA, UAG, AD, file server, AppVolumes, UEM, etc...). It's a gray area if that file server is also supporting other servers or desktops.
Always check with your VMware account team and internal legal to verify you are in compliance. Depending on your use case you might be able to just get a written exception from VMware.