Integration approach:
1/Deltek create a connector for Zendesk system,to sync ticket details
2/Customers install the Zendesk connector in Deltek
3/Customers will use the Zendesk credential to authenticate Zendesk connector
4/Customers ticket details will be synced from Zendesk,post authentication.
How to proceed with this integration approach
I hope you are well. Your use case is possible but it will fall under custom integration as we do not have a native integration with Deltek. If you are looking on where to start, this document would be helpful: Learn about the different apps you can build. You may also explore the API option here: Zendesk API quick start
You can share these documents to your Developer.
Best,
Paolo | Technical Support Engineer | Zendesk