Hi,
If you are having the same problem to access vSphere Web Client 5.5 on GNU/Linux like me, here you solution, only for Google Chromium.
For debian:
https://packages.qa.debian.org/p/pepperflashplugin-nonfree.html
For Ubuntu:
https://launchpad.net/ubuntu/+source/pepperflashplugin-nonfree
Ok!? 