I have two licences and dongles. One license and dongle installed on two workstations. I am unable to add the 11th node when submitting a distributed rendering job. I have both of my licences available in my client license settings on all machines.
I think this concerns only file sharing connections; V-Ray DR uses TCP/IP as the network protocol and you can certainly have more than 10 of these at the same time.
So that would mean you could use more than 10, without server-OS, if you make sure that a maximum of 10 nodes point to the same share for textures etc.
For example: a copy of the resources/textures on the 11th node could then be shared for the next 10 nodes. UNC-paths can’t be used then, you need to use mapped drives.