Creating a new TOAD model requires the declaration of the specific DBMS which is the implementation target. Once made, there seems to be no option to change this selection. Therefore the design created in each Toad model appears to be specifically for the declared DBMS and no other.
Many features are DBMS platform specific.
Toad Data Modeler requires you to specify target database platform, because every platform is supported in detail. You can specify Sequences in an Oracle model, however in a MySQL model, Sequences don't exist. That's why you need to choose the platform in advance.
There is a way how to use your Oracle model and generate SQL code for MS SQL - you can just convert the model from Oracle to MS SQL (or any other database platform). Please look at the Sync & Convert Wizard in the File | Sync & Convert menu. Conversion is simple and Toad Data Modeler will convert data types for you (in special scenarios also Sequences/Autoincrements etc.), but stored procedures, triggers etc. cannot be automatically converted - due to differences between database platforms.