There is a host ID per license manager - that License Manager is WebLM.
System Manager currently has a License Manager/WebLM built in - you should use that and only that unless you have certain apps like Experience Portal that need data center failover and is a totally different discussion.
The license manager has a host ID - you license all your applications to that one host ID, and then you point your applications to that license manager.
You can install any CM, SM, voicemail, whatever. So long as you have a WebLM with valid licenses against the WebLM hostID, you can change whatever CM or SM you want, so long as you point those applications to the WebLM. If your WebLM dies and you install a new one with a new host ID, you'd need to re-host your licenses through Avaya's licensing portal called PLDS to acquire new licenses. Typically, your business partner would do that for you.
Before VMWare, every physical server with System Platform could have a WebLM, and the HostID was the physical MAC address of any of the NICs on that server. Typically, you'd apply the license for a product to the WebLM HostID (physical MAC) on the physical server that application+webLM instance resided on.
System Platform was Avaya's homebrew Xen-based virtualization platform - like VMWare. Avaya's System Platform included a WebLM where VMWare did not. This means that in a purely VMWare environment, you won't be able to host licenses on the hypervisor hosting the virtual machine where you used to be able to do that with System Platform.
Short version is that you should just use the host ID in System Manager and every Avaya application you're running that needs licenses will have a way to point to a WebLM IP, and you should just put in the System Manager IP.
