I am using Viveza2 as well as all of the other Nik plugins with PSPX3. These worked in PSP X2 as well.
The only problem I have encountered with Viveza2 is the preview/work images are desaturated (very little color), but they turn out fully saturated within PSP once the Viveza2 screen disappears.
You need to put your entire Viveza 2 plugin folders (decompressed) in (program files)(Corel)(Corel Paintshop Pro)(X3)(Plugin). CREATE THIS FILE YOURSELF.
Go into PSP X3, choose <file><preferences><file locations>, click on plug-ins in the file types area, under plug-in folders check enable plug-ins, click the add button, navigate to the folder that you created above. Click OK. Shut down PSPX3 and restart. The plug-ins should now be under <Effects><Plug-ins>