Al,
to use DNN with another Database server you need to adopt all install scripts and create custom data providers for the core framework and all module - due to the effort needed, there is (AFAIK) only one company providing an additional data provider (for Oracle), any other attempts have failed.
The conversion tools you mentioned will not be of great help, because they simply transfer databases from one server to another but do not adopt the code to access the database nor create adopted SQL scripts for generation or upgrade, which can be installed as a package.
Depending on the options of announced "Linq to Entities", this possibly might provide an option for DNN in the future, to become more DB agnostic and allow for an easy change, but this will require a lot of code modifications and investigations by the core team and weigthing pro and cons and I would not expect any solution within the next year.