You can run a validation on CSB built sites.
Trellix and CSB sites will come back with multiple errors, coding issues and problems.
But then again, try to validate a page on the Microsoft website and you get tons of issues too.
No reason to run validation on CSB sites unless you plan to MANUALLY EDIT ALL HTML from that point on using an HTML editor. If you change anything in the CSB generated code, then go back to CSB to update your site, you will erase all changes you manually made.