I have Studio One 3 Artist and have also purchased the add-on pack that enables 3rd party VST support and MP3 export. I also have been using EZDrummer 2 without any issues with Studio One 3. In fact, I've not had any issues with any any of my 3rd party plugins, including Amplitube4, SampleTank3, MODO Bass, etc.
When I first was looking to purchase Studio One 3, I saw that post as well and I was also concerned, but I've had zero issues.
Hope that helps...