This article confirms whether IP monitoring is supported for IPv6 destinations, and suggests an alternative method that can be used equally effectively.
IP monitoring is not supported for IPv6 destinations.
As an alternative method, IPv6 destination addresses can be configured for an IPv6-based RPM probe. For more information about the supported Hardware/Software Matrix and using RPM probes in SRX devices, refer to the following:
Configuring IPv6 RPM Probes
Guidelines for Configuring RPM Probes for IPv6
RPM probes with IPv6 sources and destinations