Is it possible to build a custom POS integration and not list it on marketplace?

We know several restaurant chains who have custom POS systems. We'd like to build custom integrations to them and use Deliverect to connect ordering channels to them.

Is it possible to do that without listing a marketplace app?

In other words, is it possible to create a POS integration app with Deliverect that will go in production but will not be a marketplace app?