It is possible and there are a number of ways to go about doing this, all of them requiring that you can write code or find someone willing to write it for you.
One option would be to send your content via ajax to admin-ajax.php along with any wanted authentication tokens … and then listen on admin-ajax.php and process accordingly.
Another would be to create your own endpoint that checks for particular post data and then, if it looks correct, loads wordpress and adds what you need. For this you might search for bootstrapping wordpress or look at index.php in the wordpress root directory and see how it loads wordpress … then do the same when needed.
There are probably a lot of other methods as well, but those two are relatively simple to implement and would do what you want to do.
Also, you might check out wp-api.org, which I just stumbled on via a post from kaiser on a different thread here.