Do you want to use the externally created objects in your mendix application?
There is a very high risk of breaking stuff and this is not recommended.
I think the easiest and clean solution would be the creation of a webservice in your mendix application that can be used by your other application to create the database objects. With this solution, you can use your mendix application to do all the database work and it will stay consistant, and the other app for generating all the needed data.
Never create records in the Mendix database outside of the control of Mendix, Mendix needs full control of it's own database. There many ways to integrate external data: reading from an external database, webservices, csv import, excel import etc. Use these instead.