Hi,
IoT (Internet of Things) is so broad that I can not be sure if I should answer with yes or no.
NS-3 has already implemented several communication technologies that are used for IoT.
In principle, it is not NS-3's ability to be tested, but the user's/developer's ability and time that are tested...
So, I would reverse the question, what exactly (protocols, netdevices types etc) are you looking for?
Regards,
K.