I phoned support today to try and resolve the non-functional system activity lights on a 2009 Xserve (which do work in 10.6/10.7),
I was told that "No, they are not supported by Yosemite".
They have pulled the support for this function for an unknown reason.
Hope this helps anyone looking to diagnose why theirs aren't working either.
Xserve, OS X Yosemite (10.10), null
