Take a look here. This shows how to set up an SNMP server on the PI. You can then use the SNMP binding to monitor the temperatures.
I do exactly this with my Synology NAS with the following item settings -:
Number NAS_Temperature "NAS CPU Temperature [%.1f]" <network> { snmp="<[192.168.2.1:public:.1.3.6.1.4.1.6574.1.2.0:60000]" }
Number NAS_SystemFanFail "NAS System Fan [MAP(NASFanState.map):%s]" <network> { snmp="<[192.168.2.1:public:.1.3.6.1.4.1.6574.1.4.1.0:60000]" }
Number NAS_CPUFanFail "NAS CPU Fan [MAP(NASFanState.map):%s]" <network> { snmp="<[192.168.2.1:public:.1.3.6.1.4.1.6574.1.4.2.0:60000]" }
Number NAS_UPSLoad "NAS UPS Load [%d %%]" <network> { snmp="<[192.168.2.1:public:.1.3.6.1.4.1.6574.4.2.12.1.0:60000]" }
Number NAS_UPSBatteryLevel "NAS UPS Battery Level [%d %%]" <network> { snmp="<[192.168.2.1:public:.1.3.6.1.4.1.6574.4.3.1.1.0:5000]" }
Number NAS_UPSCPULoad1 "NAS CPU Load (1min) [%.2f]" <network> { snmp="<[192.168.2.1:public:.1.3.6.1.4.1.2021.10.1.5.1:30000]" }
You’ll need to change the IP address to your PI (you might be able to use localhost) and you’ll need to ensure the OIDs are correct (that’s the long number after the public word) - the link above had them I think. The number on the end is the polling period. Depending on what the Pi supports, you can monitor quite a lot using this system (you just need to find the OID)…