You would probably need to do this with jQuery by detecting the hash value and activating the class based on that. Something like this might work:
add_action('wp_footer', 'custom_review_form_activate');
function custom_review_form_activate() {
echo "<script>if (window.location.hash == 'review_form') {
jQuery('.reviews_tab').addClass('active');
}</script>";
}
(Of course if your theme or customizations already have some jquery you can add it there instead of in the footer like this.)