Obs use 32Bit or 64Bit and NDI is installed where you have OBS installed, So which ever one you run would see option for NDI once follow steps how to install it.So basically it would use 32 or 64 unless I am missing something. Should see NDI when go to Tool > NDI Output even using 32Bit or 64Bit. If you dont see it listed, need to make sure everything installed correctly