Can 2 mobile devices detect each other's presence using NFER technology? If 2 mobile devices are in the same room can they identify each other or detect the presence of each other by using Near-field electromagnetic ranging (NFER) technology ?
And the second question is what technologies give  such an opportunity at all ?
When I understand the Wikipedia article on NFER correctly this requires special hardware that is not yet present in Smartphones. Therefore this questions seems theoretical to me (which means that it is Android independent).
Regarding your question what other technologies can be used to detect devices in the same room I would like to reverse the question:
What other technologies can not be used for such a purpose. Using some creative use of technologies like Bluetooth, Wifi, GPS, NFC, mobile network you can for certain use cases invent usage schemes that allow to detect devices nearby.

NFC (hold devices next to each other)
Accelerator sensor + mobile network (&quot;bump devices to communicate&quot;)
Wifi (open a mobile hotspot, or Wifi-direct)
GPS + mobile network: devices with the same location
Bluetooth - devices in range
Speaker + microphone: use audio tones with frequencies non-recognizable by humans to communicate between devices
...

Nearly every sensor or technology provided by an Android smartphone can be used to establish a communication between two or more devices, depending on the sensor, the situation, the devices and so on. You just have to be creative and know the limitations of each technology.