You can get SNMP polling info for your hosts and VMs if you'd like via NMS. Also, if you've got Solarwinds Orion NPM product, you get a ton of great info on the whole VMware environment. You should check out vCenter Operations, which you can get a 30 (60?) day trial for. It's a small virtual appliance that you deploy and interfaces with your vCenter cluster. It gives tons of great information on every aspect of your virtual environment including storage IO.