I actually had the exact same question. So to clarify, having “VST Plug-in effect support” does not equal support for VST instruments such as Superior Drummer?
From the Sony Vegas feature list >
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VST Plug-In Effect Support
You can use effects to manipulate the audio components of your project. The included audio plug-ins can improve the quality of the audio in your project or create unique sounds. Vegas software supports additional DirectX and VST effects from a variety of vendors. Audio effects can be applied to all events on a track, to busses, or as assignable effects.
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