Please try the following, I think having a return from the site_url() function could be creating a problem with the $confirm_url variable.
That and you have an unescaped slash in your url.
$site_url = site_url();
$confirm_url = $site_url. '\/verification?id=' . $post_id . '&hash=" . $hash;
// Send a verification e-mail to the user to confirm publication
$subject = "Please confirm your Slicer Profile submission';
$body = $confirm_url;
wp_mail( $profile_email, $subject, $body );
You might need to switch to magic-quotes too, ie:
$site_url = site_url();
$confirm_url = "{$site_url}/verification?id={$post_id}&hash={$hash}";
// Send a verification e-mail to the user to confirm publication
$subject = "Please confirm your Slicer Profile submission";
$body = $confirm_url;
wp_mail( $profile_email, $subject, $body );
The parenthesis around the variables in the double-quotes aren’t necessary, but some devs find them easier to read in long strings.