Are you referring to this command?
wsewsdl3.exe /n:Vim25Api /type:webClient /l:CS %WSDLHOME%\vim.wsdl %WSDLHOME%\vimService.wsdl
That is an extremely old reference and is not required to code vSphere in C#. All you need to do is install powerCLI on your dev box from here: https://developercenter.vmware.com/tool/vsphere_powercli/5.5. You can choose the version based on what version of vCenter you are using. I used this link because you mentioned 5.5. After installed, go to your project and "Add Reference" and navigate to "C:\Program Files (x86)\VMware\Infrastructure\vSphere PowerCLI" and choose "VMware.Vim.dll". Then add a "using" statement and you can code in vSphere.
Let me know if you have any other questions regarding vSphere SDK because I have a lot of experience coding in this and most of the online references are for Java.