When you configure the broken link checker to look for urls in the custom field named _product_url, BLC would find all these links. Unfortunately, this only works for posts and pages, but Woocommerce stores its products as product.
So, in order to make these plugins work together, you should add the post_type 'product' to both line 441 and 478 of broken-link-checker/modules/containers/custom_field.php
Guess it would be better if the plugin asked you which post_types should be included.© GeekLabInfo Making broken link checker work with Woocommerce external products is a post from GeekLab.info. You are free to copy materials from GeekLab.info, but you are required to link back to http://www.geeklab.info