Hi Chris,
it is possible, but not recommended or supported (depends on your requirements). See SAP Note http://service.sap.com/sap/support/notes/73606
e.g.
"2. As of release SAP NetWeaver 7.0 Unicode is the default for all new installations of Single Code Page systems
3. Unicode is the mandatory system type: ...."
If your requirements fall under point 3, then you need to go ahead with Unicode.
Regards,
Hannes