Why would this be an accessibility problem? I don't see why screen readers would have a problem dealing with it - for them the form in the users browser will appear just the same as it otherwise would.
2.) Screenreader users have a shortcut key to submit the form - typically when under-qualified web developers create forms without submit buttons. This fires the form submit event, which without a JavaScript preventDefault will get the form contents sent to the URL mentioned in the action attribute on the form. So the screen reader user's comment is treated as spam.
In this case though, from an accessibility point of view there are a few issues with the use of a link tag rather than the standard form 'input submit' or 'button'.
Problems include:
- It goes against user expectations of how the form functions
- User would not be able to submit the form while focus is on one of the inputs (although this could be remedied with more js)
- User would have to realise that this form does not have a standard submit button and realise that the link tag is the submit button (difficult for screen readers because there are no alt tags).
There is also an issue with usability for the few who don't have js enabled, as they will not be able to submit this form.