As per the portlet 2.0 spec, it should work. The portlet container must support this. Extract from Spec..under PLT.2.5 Compatibility section.
"The Java Portlet Specification V 2.0 does not break binary compatibility with V 1.0. This
means that all portlets written against the V 1.0 specification can run unchanged. Portlet
V2.0 containers must support deploying JSR 168 portlets and the JSR 168 deployment descriptor. "