Can I use the VSP Designer without the VSP Engine Tools?

Yes, the VertiGIS Studio Printing Designer retains the ability to create templates that print using the Chromium engine on your on-premise VSP server.

However, these templates are not PAGX-based layouts, will not print with using the new VSP Engine, and cannot be opened in ArcGIS Pro. The VSP Engine Tools must be installed in order to enable the 'ArcGIS Pro Layout Mode' in the VSP Designer to allow conversion of templates and creation of PAGX-based layouts.

See this article for more detail on how to convert existing VSP templates into PAGX layouts: https://support.vertigis.com/hc/en-us/articles/18561553425554-How-to-Convert-VertiGIS-Print-Templates-to-Layouts-for-the-VertiGIS-Studio-Print-Engine