A DocuWare Professional Server License allow you to install the DocuWare Services on one machine only.
A DocuWare Enterprise license will allow you to install the DocuWare Services on two machines.
Therefore, to install DocuWare on 4 different servers, will require the customer to purchase 4 Enterprise Servers.
Simply installing a single Professional Server license on 4 machines would be a breach of the licensing agreement, and the servers will not be able to communicate with each other.
I suggest that you take the discussion up with your Regional Sales Director.
Senior Director Support Americas