It is kind of a big deal, but Apple let everyone know about it months ago.
The Endpoint Protection team was able to deliver an update last week that added 10.11 support.
All you need to do is switch from /usr/bin to /usr/local/bin as your default location for everything. If I update the Altiris config file for that location and then run:
/opt/altiris/notification/nsagent/bin/aex-configure-bin -configure
I can at least get the agent to startup on Mac OS X 10.11.
All the sub agents fail to install, but if you guys simply do a global replace on the source code to point to /usr/local/bin instead of /usr/bin and re-complile I would expect you would be nearly done.