The InsightVM-ServiceNow integration is included in the InsightVM license and doesn’t need to be purchased separately. With the integration, you can easily connect your vulnerability management with your ServiceNow to automatically create tickets for remediation tasks.
Quite new is that you now can also integrate with the ServiceNow CMDB:
With InsightConnect you can create custom workflows using 300+ plugins in 3rd party products (including ServiceNow). This is a separate InsightPlatform module and needs to be licensed by workflow or as an add-on to your InsightVM license. This enables you to use product APIs like the ServiceNow API without having to write the code yourself as you can just use the pre-built plugins and actions.
So the InsightVM integration solves one (or with the CMDB integration two) specific use-cases, while you have more flexibility with InsightConnect and can also include other products (e.g. send a Slack/Teams message after you created a ticket).