Recommendations for supporting both Oracle and MSSQL in the same ASP.NET app with NHibernate

Our client wants to support both SQLServer and Oracle in the next project. Our experience comes from .NET/SQL Server platform. We will hire an Oracle developer, but our concern is with  the DataAccess code. Will NHibernate make the DB Engine transparent for us? I don't think so, but i would like to hear from developers who have faced similar situations. 

I know this question is a little vague, because i don't have Oracle experience, so i don't know what issues we will find.

Recommendations for supporting both Oracle and MSSQL in the same ASP.NET app with NHibernate
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Our client wants to support both SQLServer and Oracle in the next project. Our experience comes from .NET/SQL Server platform. We will hire an Oracle developer, but our concern is with  the DataAccess code. Will NHibernate make the DB Engine transparent for us? I don't think so, but i would like to hear from developers who have faced similar situations. 

I know this question is a little vague, because i don't have Oracle experience, so i don't know what issues we will find.
