I've got no experience using Oracle, but conceptually I see no problems. Just make sure you use a unique schema for your Mendix data, to prevent any interference with the existing schema's.
In Oracle, each user has its own schema. When you create a specific user for the Mendix application, I think it is not a problem. However, make sure only Mendix connects to the Oracle database with the credentials of this specific user. Mendix removes all non-Mendix tables within its own user schema.
Please note that in SQL Server and PostgreSQL, a Mendix application must have its own database. Mendix removes all non-Mendix tables within this database, regardless of their schema.