Is there a Thingworx API for the ECS off the shelf MES tool?

When asking these kind of questions, it is always helpful for the reader when there is a link to the referred system included, so they know what the system in question is. Also describe the use case so it becomes clear what kind of communication you have in mind and in which direction.

Integration is always a story of two parties and the interfaces they offer. For Thingworx I can say that at least the REST interface is generic and easy to use for pushing data. There are other ways of integration, but it depends on the use case what makes sense.