IO counts are reported in VMware vCenter are reported as disk.numberRead.summation and disk.numberWrite.summation. These values are brought into Veeam Monitor through the API and can be converted to IOPS by dividing by the sample window. If you want total IOPS and you have an hour view, take the total of your read operations and write operations and divide by 3600 to get to IO per second. If you want IOPS for either category, you divide the appropriate counter by the 3600 value.
Just be sure you are aware of the period of the sample. Here is a reference to the VMware wiki with an overview of the performance counters. http://communities.vmware.com/docs/DOC-5600