The 1st part, ICMP, is built in. Just add the device to Libre (with SNMP disabled) and you’ll get it.
The 2nd can be done manually (100 times) or with the new service templates that are being developped these days. Seems that stability is not there yet so you should probably wait a few more days/weeks to get it right.
of course you can. Cameras may be autodiscovered (via ARP for instance) so you can let LibreNMS add them. Check if the cameras have SNMP support. If yes, you may be able to do your checks via SNMP