No. It is not necessary to install KeyShot Network Rendering Manager and Luxion License Server (Floating) on the same computer.
These two applications can be installed on different computers as long as your setup fulfills the criteria below.
KeyShot Network Rendering Manager is responsible for accepting and managing the jobs that are sent to the network. For more detailed information about KeyShot Network Manager, you can click on this link here.
Luxion License Server (Floating)
The Luxion License Server (Floating) is responsible for managing the actual floating license.