Hi,
Yes, it could be that the Health monitor ICMP hosts field is looking for IP specifically and it just fails to parse full hostname. But you can always ping that hostname through CLI or anything else and that should reveal the IP address at the end of the ping, use it as your hostname instead.
One more recommendation would be to use popular DNS server addresses with your pings and fields that check the IPs to determine the internet connection, as those addresses, like 8.8.8.8, 1.1.1.1 and so on, always stay the same.
EB.