Remember that VST isn't a plug-in spec, it's a spec for communication with the host. If the host implements the spec properly, and so does the manufacturer, it's going to work.
 
However like MIDI, just because something is in a spec doesn't mean it's implemented. For example the VST3 spec allows to suspend operation if the plug-in doesn't have audio passing through it, which can save CPU power. However, both the host and plug-in need to support this feature.

Also not on their "supported" list: Mixcraft, Wavelab, Samplitude, Digital Performer, MuLab, Pyramix, and Harrison Mixbus.
 
Whatever. Last time I checked, iZotope were licensing their technology for inclusion in both Mixcraft and Cakewalk, and Ozone Elements 8 works great with both programs on my systems.

We're having conversations with a lot of 3rd party companies to get them up to speed, make sure marketing is updated (SONAR -> CbB) and that any internal ways in which they used to detect/provide support & integration hasn't broken as part of the switch to a new application & registry files :-)
 
Sorry for the inconvenience in the meantime, and support staff do take a while to catch up!

The day iZotope plugs no longer work in CakeLab is the day I must find a new DAW. I've spent way more with iZotope than with Cakewalk in the last 5 years. Fortunately, I don't believe iZotope will stop working for me in the near future, and think Cakewalk is on very solid ground right now. As for the OP's question about support by third party manufacturers . . . we simply have to allow more time to pass, it's only been a matter of months.
Things evolve in the programming world much slower than things evolve in the marketing world.
 
In my hypothetical world . . . if I was a newb, and if I was shopping and testing all the DAWs right now, the choice would be obvious. It's just a matter of time until all the third party manufacturer's take notice.