Are you referring to another server role, such as already having an ArcGIS Server component (Image, GeoAnalytics, GIS) installed on the server? If so, that may be possible but not recommended and likely not Supported by Esri. The Notebook Server role is different from the others and uses computer resources differently. Trying to run it with another intensive program can lead to poor performance and instability on that server. It does get installed on a Server in the sense that is an Operating system with dedicated hardware (CPU/RAM/NIC), but the server must also meet certain requirements such as the Hyper-V role for Windows servers. Before Jumping in to using Notebook Server, get familiar with the installation requirements and process as well as how the product works. That will help guide your decisions when planning how to set it up. The documentation can be found here.