"Version 5.0 is required for the Large and Extra Large OVAs. Version 4.1 will work with Small and Medium OVAs, but 5.0 is preferred. Prime Infrastructure 1.3 has not been tested with VMware ESXi Server versions later than 5.0."
There hasn't been a major release of Prime Infrastructure since 18.104.22.168, so no, a new version that MAY support VMware ESXi 5.1 would not have been made available yet.
If you need this ESXi 5.1 or later support, please contact your Cisco SE, Cisco account team or Cisco authorized wireless reseller, and discuss it with them. The sales side of Cisco has procedures in place to accumulate customer inputs like this across all the customers they serve, and to get that input forwarded to the various business units within Cisco for possible inclusion in future releases of Cisco's products.