i agree with merrill that there are certainly limitations to the validation framework and from time to time you'll have to ask yourself whether or not it's worth it.
in your case, since you are using javascript for validation, why not just skip the validation framework all together? i never understood why people use the validation framework for javascript validation at all. it's cumbersome and adds lots of redundant js into your codes. this is not to mention the cross-browser compatibility, especially when you start adding your own validation.
struts 1.2.x improved this quite a bit (i believe), but i still firmly believe i can write simple (shared) js validation more efficiently.
with that said, the validation framework is an extremely powerful tool and wonderfully designed for expandability for server-side validations. there IS a learning curve, but once you get over the hump, the world is in your hand. i think i've encountered many, many types of strange validations and have been able to tackle them all using the framework declaratively. there are a couple of cases i could think of that i had to pull the validations INSIDE the action classes and use struts message handling instead. still, messaging, if set up correctly, interact well with validation error display to create a seemless 'validation'.