In emberGetLastHopRssi() the RSSI value is of data type int8s, which is the RSSI energy level in dBm.
For EmberZNet PRO releases prior to 4.0.2:
In emberEnergyScanResultHandler() the RSSI value is of data type int8u. This is the raw RSSI value straight from the radio, which is offset by -154 from the actual dBm value measured. So simply take your unsigned 8-bit result, subtract 154 from that, and that is the RSSI energy level in dBm for that channel.
For EmberZNet PRO releases 4.0.2 and later:
In recent releases, emberEnergyScanResultHandler() returns the same kind of int8s (representing actual RSSI value in dBm) as in emberGetLastHopRssi().