How to access Vmware Esxi Server from Ubuntu 12.04.1
The vSphere Client is only available for Windows systems and it is not available for Linux systems.
The solution is to use vSphere Web Client.
More info in the VMware Knowledge Database.
We had the same problem and our resolution was to run a Windows VM on our Ubuntu machines purely just to be able to run the VSphere Client
VMware player is a free download. Something to note, it is quite resource intensive and requires at least 4 GB of RAM to run smoothly on Ubuntu.
Link to download VMWare player