Is there a way to low level discover snmp items that do not follow any index? Well there is some index, but the rest after IP-MIB::ipNetToMediaPhysAddress.20000{INDEX} is an IP that it is associating the MAC address with on the switch (arista if that helps).
Here is some examples from my snmpwalk with a couple of translations:
$ snmpwalk -v2c -c public localhost
IP-MIB::ipNetToMediaPhysAddress.2000010. = STRING: 0:10:86:80:3:11
IP-MIB::ipNetToMediaPhysAddress.2000011. = STRING: c:c4:7a:65:bb:d0
IP-MIB::ipNetToMediaPhysAddress.2000012. = STRING: ec:f4:bb:cf:d9:ba
IP-MIB::ipNetToMediaPhysAddress.2000100. = STRING: c:c4:7a:1f:7a:12
IP-MIB::ipNetToMediaPhysAddress.2000999. = STRING: 0:86:9c:16:be:53

$ snmptranslate -On IP-MIB::ipNetToMediaPhysAddress.2000010.

$ snmptranslate -On IP-MIB::ipNetToMediaPhysAddress.2000100.