In Studio One you will want to make sure that you've added the Universal Audio plugins directory to Studio One > Options > Locations > VST Plug-Ins.
For Windows this will vary depending on if you are running the 32-bit or 64-bit build of Studio One.
For 64-bit use:
C:\Program Files\Universal Audio\Powered Plugins\UAD-2 Powered Plugins
For 32-bit use:
C:\Program Files (x86)\Universal Audio\Powered Plugins\UAD-2 Powered Plugins