I've produced my own version of Sqldoc for RedShift, Vertica and MySql using Python, Pandas and Sqlalchemy libraries.  Due to the way I architected the solution adding another DB platform is a case of adding the driver name to the list of drivers in the build file, writing 4 queries that conform to a known contract and an extra case statement in the thing that chooses the driver to use with Sqlalchemy.
The tests all work as before.  It took 15 minutes to add support for an additional DB platform.

Obviously I don't know what the source code or architecture of the rest of the Red-Gate tools are but I would be looking to see if .NET core covers the functions I need.  . NET core runs on Linux & Macs.  The trick is to design something where the cost is mainly in first implementation and subsequent implementations are quick and therefore cheap.
I know that DG relies on tabular data streams but I don't know if that's in .NET core.