OK Jason - I have figured this out by finding a forum post that tells me I have to have eCart 6 to have the menu entry point for JQuery validation, so I have added and adjusted in the field bindings panel.
But I discovered that although the validation worked fine on a blank page, soon as I added my Bootstrap template, the h5validate stopped working.
So in the meantime I have tried the bootstrapvalidator.com validator (I am obviously using Bootstrap for this site).
This actually seems to work really well - BUT when I added the WA Validators to the form, they don't seem to work - especially worried about the Captcha.
Any ideas on this?