To make asssu obey wp table prefixes a following patch asssu-models.php should do the trick:
262c262 < $config->db_table = $wpdb->prefix.'asssu_endpoints'; --- > $config->db_table = 'asssu_endpoints';
And after this, two wp instances having asssu installed can run from the same db.
On the other hand it seems like this would be also possible if the id table would be dropped and the pk would be the site_url field instead.