Executing embedded migrations fails for included file
The DbUtil project that you're advising to use has multiple problems:
1. Executing embedded migration not using SQLCMD variables (see https://forums.red-gate.com/viewtopic.php?f=199&t=80411)
2. Included files with relative paths are not executed (this post)
It seems poor form to provide advice to your customers to use a tool, when you have not tested that tool thoroughly yourself.
I will submit a PR to the project for a fix, but it's disappointing to run into these issues and have to fix them myself.