In MyEclipse, our REST web service support is based on Jersey (JAX-RS RI) which does require Java 1.5 to function. It appears that in WAS 6.1 / RAD, the REST features are achieved through JAX-WS which can work with Java 1.4.
We will take a look at addressing this shortcoming in the 11.1 release; I’m afraid I cannot suggest any other workaround now. Thank you for bringing this to our attention.