I wouldn't make that assumption. Do check return codes and load times, and back off if you see issues. If these sites are business partners/suppliers you have

I wouldn't make that assumption. Do check return codes and load times, and back off if you see issues. If these sites are business partners/suppliers you have a lot to lose if things go wrong. It's worth it to develop your relationship with the business owners of the services you're touching in the correspondent organizations. And do set a User-Agent string that declares who you are and provides a link for information; if you are doing business with them, it should be on a basis of honesty.