Hey @hilariouscow ,
When linking Rivet into a scene, link the RIVET collection not the Rivet_rig. This will give you the GEO (geometry) and the rig.
To use the rig you next need to make a proxy.
To do this immediately after linking the RIVET collection, click OBJECT > RELATIONS > MAKE PROXY and select Rivet_rig from the pop up.
Now you can switch to pose mode and animate Rivet.