I believe the smart meter uses Zigbee to the IHD. It is not clear what Zigbee profiles are being used, it could be Zigbee Smart Home Automation 1.2 and Zigbee Smart Energy 1.2 profiles or just ones of these.
I thought no-one had discussed this topic here I even did a search in the forum but it turns out (via Google) there has already been discussion about this.
See Can I integrate my Zigbee Smart Meter With SmartThings? as one example.
It seems Samsung Smartthings is being rather backwards in not supporting the Zigbee Smart Energy profile (and probably others).
Hmm, it turns out there is a Zigbee 3.0 standard which acts as a ‘meta’ standard meaning it contains the previous individual Zigbee profiles. This means in theory a compatible device would then support bother Zigbee Home Automation and Zigbee Smart Energy. The Smartthings Hub v3 is listed as a Zigbee 3.0 device. (The Hub v3 is not yet available in the UK.)