You can run 2 Oracle instances with the same database name. To do that set the following parameter(s):
Instance 1:
*.lock_name_space=DB1
*.sp_name=DB1
Instance 2:
*.lock_name_space=DB2
*.sp_name=DB2
In your oratab you would have two entries, one for DB1 and another one for DB2. db_name would be the same for both.