If Tableau / Tableau Server cannot request data from the SQL box in your Process Network, you'll need to create some sort of a process in that network that packages up the data from SQL Server and ships it to the Business Network.
I'd suggest you investigate:
- An ETL process that exports relevant data from the Process Network database and imports it to another SQL Server in the Business network
- Using the Tableau Extract API to export portions of the data from SQL Server in the Process Network. You'd then need to come up with a way to copy it over to the other network where you could publish it to Tableau Server via Tabcmd. See: Tableau Data Extract API and tabcmd Commands for more information.