"Can client systems access a license server from a different subnet?"
No. All clients using a license server must be in the same tcp/ip subnet as the license server. In addition, for a redundant server configuration, all license servers must be in the same subnet as well.
I don't understand why it needs to be on the same subnet. We have an internal network setup where we have developers on many different subnets. I want to setup one license server for everyone but the above documentation indicates I need to install a server for every subnet? This scales very poorly - how to large organizations deploy vtune?