I think vistadb can be used with sql server queries, but the metadata for the driver is likely not compatible. So for the queries at runtime, you likely can just use the dqe of sqlserver, perhaps change it a bit to make it use the vistadb factory and e.g. not emit catalog names in the output.
The sourcecode of the dqe's is shipped with the installer and also available in 'My account -> Downloads -> version -> Extras section'. It also contains the sourcecode of the drivers.
As it's a db we don't natively support, there's always some detail that might take a while to implement. We can't assist in this matter so you have to deal with setbacks yourself, but as the sourcecode of all drivers + DQEs is available to you, it should be reasonably straight forward. I'd start with the SQL Server DQE and see what to change to make it work on vistadb. Keep in mind that with catalog/schema overwriting using name -> "" you can already remove schema/catalog names in the queries that are generated.
