Just as extra data point:

It is fairly common to have a common exception class which is then used a mixin class together with the standard exception classes, so that you can indeed identify the source of an exception and catch errors based on the source (e.g. say you want to catch database errors coming from MySQL specifically).

The Python DB-API also requires to create a separate hierarchy for this purpose.

Overall, I wouldn't call this a non-best practice. It depends on the use case, whether it's useful or not.