Error: Call to a member function get_error_code() on a non-object

Your function must return the variable $errors – even when there is no new error in your logic.

'registration_errors' is a filter, and filters always expect a return value. Without that your function returns NULL, and that is what var_dump() found.

So the basic function body should be:

function add_user_to_SF($errors, $sanitized_user_login, $user_email ) {
    try {
    } catch (Exception $e) {
        return $errors;
    }
    return $errors; // important!
}