Hello Mimik,
It's true as you read that you can use the LabVIEW Simulation Interface Toolkit to make a user interface for your model. This will work regardless of the contents of your model - it will work fine if your model uses a library that you have created yourself.
It's not possible to export your library to LabVIEW, or to create a new model from LabVIEW. However, if you want to create a model of your system in LabVIEW, you can use the LabVIEW Simulation Module, which lets you create and run simulation diagrams entirely in the LabVIEW environment.
Take a look at ni.com/simulation has more information.
The product information page for the Simulation Interface Toolkit is http://sine.ni.com/nips/cds/view/p/lang/en/nid/11763
and the Simulation Module's page is http://sine.ni.com/nips/cds/view/p/lang/en/nid/13852
I hope this helps,
Andrew