I don't know about Dragon 11.5 but I am using Dragon 12 under Windows 8 and it starts and runs fine without admin rights although I am logged in as an administrator which is a slightly different thing. I am using the function key {F7} to switch on and off the microphone system wide without any issues.
However what I will say is that Windows 8 is a bit of a security nightmare as it has lots of new security measures implemented. It takes a bit of getting used to and if you seriously want to continue using it as your only system then be prepared for hitches along the way. I prefer to use it really as a beta test for the moment although I am now using it as my main system. However I have a Windows 7 partition to switch to at any point.
One thing I would recommend is turning off User Account Control from the control panel.
mein Englisch ist nicht das Beste .. wenn ich das richtig verstanden habe, soll ich die UAC abschalten. Das habe ich vor den Tests getan. Half leider nicht.