According to the definition about windows User CALs:
With the User CAL, you purchase a CAL for every user who accesses the server to use services such as file storage or printing, regardless of the number of devices they use for that access. Purchasing a User CAL might make more sense if your company's employees need to have roaming access to the corporate network by using multiple devices, or from unknown devices, or if you simply have more devices than users in your organization.
But here I'm not if the application you mentioned can be used directly on server.
If users remote access (RDP)the server , they can use full desktop or remote App.