Jonathan,
While it would be nice if the "required" validation
test provide by struts handled this situation, it doesn't appear to. However, the validation framework was meant to be extended, and you could write your own extension to handle this situation.
I haven't really looked into it, because I normally just write my own javaScript validation, and don't try to work with the validation framework.
However, you can add your own validators to the validator-rules.xml. Below is a url that shows an example of someone writing their own javaScript function and including it as a validator rule:
http://www.raibledesigns.com/page/rd/20030226 You could create a rule called "radioRequired" or something like that, and include a javascript function to handle it.
P.S.
I just noticed the example I gave you in my previous post was wrong. It should read:
When you have a more than one form control with the same name, javaScript interprets it as an array of controls.