As per the Snow Guide - "On the Discovery page information on discovered computers and other devices are presented in views. These computers/devices do not have an Inventory agent installed."
"A discovered device cannot be automatically deleted in Inventory. It will remain visible on the
Discovery page until either an Inventory agent has been deployed to it, or it is manually deleted in
the Admin Console."
As per the guide, the devices displayed in discovery do not have the inventory agent installed. But we can see the devices both in Discovery and Devices view. The agent is installed on the devices present in the Discovery view and the devices are reporting to Snow Inventory daily. And also the discovery results are updated every 3 days.