First, awesome and thank you. I hadn't thought of this but it seems like a great addition.
Second, would it make sense to only check the immediate parents? This code is ultimately getting called in Update of each Grip Point and scaling up the hierarchy from every Collider it touches. That's a lot of pointless traversal for objects that have Colliders but aren't grabbable. It's probably not as bad as checking children but it's noteworthy.
Is your use case is the same as described in the Compound Colliders section from the Rigidbody docs? After the merge I'd also like to add a small example in the demo scene.