Hi Dave,
from the High Availability point of view I would avoid Windows by any means.
Which Linux type are you planning to use?
SuSE Enterprise or RedHat (should be working on Oracle Linux as well)?
Migrating schemas from database vendor to another is very tricky.
I did so the other way round (from MS SQL to Oracle) last year and this is not finished yet (still requiring some fine tuning).
We used Oracle SQL Developer equipped with an additionall MS SQL JDBC driver Type 4 to copy the structure and data.
But most of this was custom data not related to the wM schemas which have been created from scratch.
Regarding the Drivers:
wMs bundled DataDirect has JDBC Type 4 (Thin Mode) support for Oracle as well as MS SQL built in.
For the JDBC Adapter there is also a Type 4 driver available for download from Microsoft, which is independent of OS.
Regards,
Holger