CBSubs provides CBSubs SQL Actions and CBSubs URL integrations. These integrations will allow you to perform a database query or execute a code file; thus allowing you to implement any integration you see fit. I recommend reviewing documentation and (for SQL Actions) the SQL Actions boards for example usage.

As for lead contacts the best I can advise is a Affiliate tracking system such as PostAffiliatePro or iDevAff, which CBSubs has an integration for both.

Can better answer your question with more details of what you're trying to do.

I don't know what software or code you're using for this leads capturing. There's not much more I can advise, if you can add the user to Site B by way of query then of course CBSubs can do it with CBSubs URL using a code file to perform the query (assuming Site B is in a different database). Sorry, am not familiar with "leads capturing", care to explain with more details?

CBSubs URL can retrieve the information of course (depends on how you code the file that's to be executed) and do whatever you like with it, but for what you're using CBSubs for it was not designed. CBSubs is designed for subscription management, not for lead capturing and management. You might want to consider a different solution if this is your primary need. To me this sounds like affiliates management, which I also suggest looking at iDevAff and PostAffiliatePro perhaps.