Accessibility implications of using a button instead of a link

I'm working on a client project which acts as a resource and support system for vulnerable people. Accessibility compliance has been touted as the absolute highest priority for this site because of the expected users, so we're currently working to meet WCAG 2.0 Level AA as closely as possible.

Currently the code for the login/registration links in the header looks like this:

<div class="profile-summary">
    <a class="profile-summary__link" href="#">Login</a>
    or
    <a class="profile-summary__link" href="#">sign up</a>
</div>

Another developer who is working on the user management system wants to change the login link to be a form containing a submit button. Something (hypothetically) like this:

<div class="profile-summary">
    <form action="/login" method="get">
        <button type="submit">Login</button>
    </form>
    or
    <a class="profile-summary__link" href="#">sign up</a>
</div>

This doesn't really sit well with me and it seems like something screenreaders and other assistive software will trip over (e.g. won't read the login option when summarising the page). To my knowledge some of these switch into a 'form mode' when they encounter a form, which would be jarring in this situation.

Are there any detrimental accessibility implications to using a form and button over a plain link in this context?

Thanks!