Yes, the steps are correct i.e to use update manager you need to connect to VCA using your vSphere C# client (windows based client and provided you have the plugin installed) and to use full feature of vSphere 5.5 you need to connect to your VCA using the Web Client.leveraging
However, I am just curious why you wish to upgrade ? Is it really required ?
As you would only be upgrading your vCenter & VUM to 5.5.. but would be keeping your ESXi host to 5.0, so you wouldnt be leveraging the full features of 5.5 anyway.
IMO.. You should wait for the next release, I'm sure in next release they will have a mature web client with update manager integrated fully
or
You can just upgrade your whole environment to 5.5 instead with different Hosts that are compactiblie with the HCL