PowerCLI 5.8 R1 does support PowerShell v2 (Or use Powersehll.exe -version 2) and you are correct the PowerCLI for Update Manager only supports PowerShell v2 and the version of VUM you have installed, we know this can be an issue and causes problems and we are looking to update it in future releases.
PowerCLI 5.8 R1 Supported PS Versions: Compatibility Matrixes for vSphere PowerCLI 5.8 Release 1