You can run multiple VST or AudioUnit plugins inside jammr at the same time.
Go to jammr's Settings | Effect plugins to add Addictive Drums 2 and Guitar Rig 5. Make sure that the Guitar Rig instance is before (above) the Addictive Drums instance.
Now select Addictive Drums and click the Route… button and select “Mix”. This will mix the output from Guitar Rig together with the output from Addictive Drums. You should be able to hear both your guitar and the drums at the same time.
If you are controlling Addictive Drums using a MIDI drum controller, remember to select a MIDI input device in jammr's Settings | MIDI.
One thing to keep in mind when using drums: make sure you set jammr's tempo (!vote bpm 120) to match the tempo your drums are playing at. Otherwise people will not be able to play in sync. More on playing in sync here:
https://forum.jammr.net/topic/1115/