Question

Do I need to buy additional licenses of NodeJoe in order to do network rendering?

Answer

No. NodeJoe simply creates materials and maps that show exactly the same way in the standard 3ds Max Material Editor, so any materials built with NodeJoe on one workstation will show and render over the network even if you don't have the plug-in installed on the network slave systems. So you don't need to install NodeJoe on your render slaves as it is unnecessary.