Many of us know that Vegas Pro doesn't compatible with VST3 plugins.
There is a plugin called "Blue Cat's PatchWork", that is working like adapter between VST2 and VST3. You just install it like you always do, add to event/track and in it you can start any VST3 plugin.
Tried with Audified SPEAKUP for sidechain compressor on two tracks))) It is only VST3.
By the way! In Vegas 13 audio is match more stable with audio editing and Faster than Vegas 17...