I am also interested, and have only run into one organization that seems to be using ZenCart and Moodle. It is a nursing school in Canada BC. I have repeatedly tried to contact them, but I get no response.
Paying with credit cards in Moodle seems to be a big topic, but no one seems to be addressing the need. There was "Authorize.net" but it has been removed. DPS is also available, but it is expensive.
I see nothing on the ZenCart side.
If you find a solution, there are a lot of people interested in combining the two systems, and would like to hear about your solution!