What happens is it seems to fool the program into thinking that the VST instrument is a DX instrument. So, the VST instrument does whatever a DX instrument would do. With Sonar, that means putting it in the FX bin and so on. When run in this way, I did notice that VST instruments could respond to tempo (if they had that capability built in, of course). However, they can't transcend limitations of the DXi spec. For example, Battery lets you assign multiple outputs, but DXi won't let you do that yet, except by calling up multiple instances of the instrument. Therefore, if you run the VST version of Battery under DXi, you don't magically acquire the ability to use multiple outputs in a single instance of the program.
VST-DX does what it does very well. I've used a slew of VST instruments with Sonar and everything has been very stable. Make sure you read VST-DX's "read me" file, though, there are some settings in Native Instrument plug-ins that have to be set correctly for things to work right.
