Can 4.0 SE & 7.1 SE coexist?

We have a client using Informix SE 4.0 on a SCO Unix system. They want to access the database with ODBC, so they upgraded SE 4.0 to 7.12, which includes Informix-Net. The problem is that their Unix application was written using the 4.0 tools and hence needs to use the Relay Module (sqlrm) to run. They are complaining that the application is now much slower, probably because of the relay module. My idea is this: On the Unix system, continue to use the SE 4.0 engine to access the database, but still run the 7.12 sqlexecd so ODBC can be used to access the database. This will avoid the relay module. However, it means that both the 4.0 engine and the 7.12 engine will be accessing the same database. We have not tried this yet, but could it cause problems (such as...)?