Hi,
You can change the line:
$query = 'SELECT * FROM '.hikashop_table('product').' WHERE product_access=\'all\' AND product_published=1 AND product_type=\'main\'';
to:
$query = 'SELECT * FROM '.hikashop_table('product').' WHERE product_published=1 AND product_type=\'main\'';
in the file plugins/hikashop/google_products/google_products.php and it will list the products regardless of the "access level" of the product.
Note however that it means that Google will reference these products. And thus users that might not be able to see the products on the website will get them on their search results on Google.
Note also that you'll loose the change when you update HikaShop in the future, so you'll have to reapply it.