Instead of SData, can it support a web services integration? If the Zoho developer can send a JSON or XML file then that is a better way to go.
The client would have IIS installed on a server which would have a web service configured. It would listen for the Zoho request to create customers or sales orders in Sage 100.
On that IIS box will be a custom dot NET program that will use the BOI to create the actual sales orders and/or customers in Sage 100.
Send me a chat if interested.
Even if it was SData it would take a fair amount of discovery, homework, and delivery time to get it done just right , regardless of what client may have heard or been told by anyone.