Final Cut Pro X uses the plug-ins located at /Library/Audio/Plug-Ins/Components and ~/Library/Audio/Plug-Ins/Components. As FCP X is a 64-bit application (with no bridge like Logic), it only accepts 64-bit Audio Units plugins. So if your UAD and Altiverb plugins are 32-bit, therein lies the rub.
You’ll have to upgrade to 64-bit plugins when they are available. I don’t believe UAD or Altiverb have 64-bit version at the present time.
So for now, you’ll have to stick to editing with those plug-ins in your DAW. FCP X really needs roundtripping… BAD.