Does someone who knows more think that the onSuccess listener may help with issues we are having with Marketo reCaptcha "submission failed, please try again later" issues?
Adding an onSuccess listener won't fix a submission error - by definition it's a different stage. I suggest opening a new thread in Products, describing your reCAPTCHA error and linking to your page.
@sanfordwhiteman Is this article still relevant? I am having issue using GTM to do the form binding and while I am not a developer, the answer to my issue seems like it might lie in this article.
Yes, this article is totally relevant. The technique here should be used on all sites with a non-guaranteed load order (but sadly people still use other broken code).