Sounds like what you want is to configure an IP SLA operation on RTR1, using RTR2 as the responder, and to have that SLA operation monitored by Orion.
The IP SLA monitoring module is an add-on module to NPM.
IP SLA is a feature of IOS but availability is dependent on the IOS version and feature set. In older IOS versions it is referred to as RTR. The types of operations that can be configured vary depending on hardware platform and IOS version, but ICMP echo operations (like you describe above) are supported on all SLA-capable versions I've come across.