It appears in 6.7, however, that the "GPU" selection in the drop-down is only available in the Flash client - I am unable to see it in the HTML client. This will at least give you overall utilization of the cards in the hosts. It may be available in 7.0 for HTML but I cannot confirm at the moment.
If you're looking at a per-VM frame buffer and GPU utilization, NVIDIA provides perfmon counters that you can utilize and remotely connect to the Windows guest machine to check them out:
