There are no prerequisites for the SCEA certification. (The reason, as you'd find in searching this forum, is that SCEA is a different job role than any of the other
Java certifications - this one is geared towards software architects, instead of software programmers.) As such, no, you do not need the SCDJWS.
Knowing about web-services and how Java implements them on a basic level would be helpful for the SCEA, but knowing how to develop one in terms of writing code is not required. (It may well be helpful, but it is not required.)