Dirt Rally (and other CM games) can only output telemetry to one port (device) at a time but, you can setup a Proxy server to forward the signals to other ports. Anyone using SimCommander can use the port-forwarding provided, otherwise, you can download one for CM games from the eksimracing website.
Aside form the port issue, I've used both DashMeter Pro and SLiMax and they work fine with Dirt Rally.