The Native Instruments should be in their own unique folder. Just remove the file path.
I would not delete or remove them just in case Native Instruments gets muddled when updating.
If it turns out that there are other 32 bit VSTs in the same file path as the Native Instuments 32 bit plugins then you will need to do some housekeeping to make sure Sonar points to the right 32 bit plugins whilst ignoring the native instruments.
You could move the Native Instruments 32 bit VSTs to another folder, but everytime you run the NI updater you will have to remember to put them back...
The real issue is the NI installer is stupid, at no stage does it give you an option not to install the 32 bit VST's, and also you've got to be careful where you install your VST's.
My VST's are stored like this, it took me a good few hours to move them so everything behaved nice. My NI 32 VST's are in the D:\AudioPlugIns\Depeciated\32bit.
Sonar does not know about the Depreciated Folder.
D:\AudioPlugIns\32bit
D:\AudioPlugIns\64bit
D:\AudioPlugIns\Depeciated\32bit
D:\AudioPlugIns\Depeciated\64bit
D:\AudioPlugIns\VST3
Just remember moving VST's can have consequences, often it's better to uninstall and reinstall. You can also hack the registry (avoid unless you know what you are doing).