Yes, it is possible to integrate ZenDesk with ServiceNow for tracking the software subscriptions..
Yes. ZenDesk has a CMDB that is a Customer Management Database.
ServiceNow helps in creating a meaningful application for the business users to route work through the enterprise. It also maintains the confidentiality and integrity of the data. Hence, is it also known as a powerful reporting tool.
No. ZenDesk is not compliant with ITIL, however, ServiceNow does.
Both ServiceNow and ZenDesk offer the same services to the customers of assets and product management using ticketing support but ServiceNow offers these services natively whereas ZEnDesk offers these services as a third-party.