Also got a reply from another person who said it worked OK and suggested adding a column to identify VST3 plugins. Thanks for that, Eurig.
Unfortunately, I don't know how to definitively identify a VST3 plugin because I don't have any. Yes, it's usually in the product or file name, but I can't assume that's always the case. So if anybody who's comfortable poking around the registry could have a look and see if there's maybe a registry key that flags VST3s, or check the DLL headers for identifiers, that would help.
Looking at the registry, I see a flaw in the program, which is that it assumes the data is under "SONAR Producer". I'm guessing the program fill fail if you're running a different edition. Maybe somebody who's running SONAR Studio could verify where the VST inventory resides for them. I'm guessing it's HKCU\Software\Cakewalk Music Software\SONAR Studio\Cakewalk VST\Inventory for 32-bit O/Ss and "Cakewalk VST x64" for 64-bit O/Ss.
Once I know every possible path, I can just have the program check them all so it won't matter which version of SONAR you're running. Currently, it just checks the 32- and 64-bit paths for SONAR Producer. It's a 32-bit program so it'll run under any Windows version.