I found this little nugget on YouTube while researching ESXi 6.0. A beta tester recorded the installation of ESXi 6.0 beta and when they went to the vSphere Client download page I was shocked to see something called "vSphere Host Client Installer for Mac".
After looking into this a little further I discovered that it was only available on a specific beta release, VMware-VMvisor-Installer-6.0.0-1921158.x86_64.iso to be exact. I obtained a copy, through the magic that is Google search, and created a ESXi 6.0.0-1921158 VM in Fusion so that I could get the installer links.
The ESXi welcome page includes the following two links to the vSphere Host Client Installers:
Edit: Links are no longer valid (6/24/2015)
I downloaded and installed the VMware Host Client and was able to connect to the 6.0.0-1921158 beta host and to my 5.5u2 lab host.