It's possible to import any draw.io diagram and then map the components as described here: Importing Diagrams.
To avoid the mapping step, you can also import the IriusRisk shape libraries into an external draw.io instance, such as on Confluence, Draw.io web or desktop versions. The shape libraries can be downloaded from here.
Once imported into the draw.io instance as a library, you can draw the diagram using native IriusRisk mapped components. When the diagram is imported into IriusRisk, the components will already be mapped, and as long as each component has a name and belongs to a TrustZone, the model can be generated.