Okay so i finally tracked it down. Seems like vRA IAAS is using the snapshotTree id for linked-clone references. If you have access to the VC:VirtualMachineSnapshot you can find the id like this:
//snap is the provided VC:VirtualMachineSnapshot you want to use as linked clone reference
var vm = snap.vm;
var id = snap.id;
function findSnap(snapTrees, snapId)
{ System.log("Searching SnapshotTree for id '" + snapId + "'..."); for each(snapTree in snapTrees) { System.log("Checking snapTree '" + snapTree.id + "' with id '" + snapTree.snapshot.id + "'..."); if(snapTree.snapshot.id == snapId) { System.log("Found matching snapshot! SnapTree id is: '" + snapTree.id + "'.") return snapTree.id; } else { var childSnaps = snapTree.childSnapshotList; if(childSnaps.length > 0) { System.log("Checking children..."); return findSnap(childSnaps, snapId); } } } return null;
}
// Get the id like this
var snapTreeId = findSnap(vm.snapshot.rootSnapshotList, id);
Hope this saves somebody some time.