In Houdini 18.0.311 and newer, a new feature was added to store any attributes of a SOP in the output gameobject as a script component (HEU_OutputAttributesStore). More info provided in the online documentation:
This is a useful feature, especially when combined with a script callback to apply those attributes right after a cook. See the included example HDA (Assets/Plugins/HoudiniEngineUnity/HDAs/HEUInstanceAttributesStore.hda) which triggers a callback to query the health values on instances and set them as y-scale. You'll need to create a Cube prefab in Assets/Prefabs/Cube.prefab before instancing the example HDA in Unity.