Is it possible to send SNMP traps to a hostname instead of an IP?

It is not possible based on the CLI commands and documentation:

[edit]

root# set snmp trap-group TEST targets ?

Possible completions:

 <target>       IP address

For each trap group that you define, you must include the target statement to define at least one system as the recipient of the SNMP traps in the trap group. Specify the IPv4 or IPv6 address of each recipient, not its hostname.



Configure SNMP Trap Groups

https://www.juniper.net/documentation/us/en/software/junos/network-mgmt/topics/topic-map/configuring-basic-snmp.html#id-configuring-snmp-trap-groups