You did not give the specific sysObjectIDs for these devices, but you will need at least RME 3.5 IDU 10.0 to support the 2800 and 1800 series routers. The AS5800 and 5850 are supported in RME 3.5 without any IDU.
However, availability works with any SNMP-capable device (even non-Cisco devices). The caveat is that you cannot have more than 1000 devices polled by availability. This assumes you have a multi-processor server with a lot of RAM.