FLStudio's plugin manager is not up to date with the latest versions of the SDK.
This was taken from the page "VST 3 Locations / Format" in the SDK documentation:
[quote]
On the Windows platform a VST 3 Plug ...
like to purchase one. Like Antares AutoTune. But before I spend all that money, I would like to make sure that it works in the Mac FLStudio.
Anyone have any AutoTune plug ins that work?
Also, maybe something like eZDrummer. ...