In our org, we have two types of accounts: businesses - with indirectly related contacts, and people (not to be confused with person accounts, no, we have a custom solution that replicates that functionality) - with a directly related contact. It's always a 1:1 relationship. (I know this isn't ideal, but it's what we've had to do to integrate with an existing home-grown system.)
In other words, we have Smith Farms business account. John Smith is a people account that is a related account of Smith Farms. John Smith is also a contact related to John Smith account, with an indirect relationship to Smith Farms. Based on what I've read about how this functionality works, if I added John Smith people account as a campaign member and used the send list email functionality, then the John Smith contact would receive an email. However, if I add Smith Farms business account, nothing would happen.
I'm also curious how this works with Marketing Cloud. If we already have a subscriber for John Smith contact and we then add John Smith account to a campaign to pull into a marketing cloud send, then does the subscriber end up duplicated?
Jenna Weiner (AgWest Farm Credit) 
Forum Ambassador
Well, maybe this doesn't work how I'd expect. I tried it in a sandbox with sending to an account that did have a directly related contact and it failed to send. Email said: "List email "Testing sending to account campaign members" was canceled due to an error detected by the system.
Error code: NO_RECIPIENTS
Error Description: No recipients provided by the ListEmail
Click https://brave-panda-al3hlg-dev-ed.my.salesforce.com/0XB8c000000TzQX to view more details about this list email.
Salesforce List Email"
