i guess you are not realy into ARTNET, because it is just the question of how you set up your ARTNET.
To split the ARTNET you need a Network-Switch and the following IP's and Subnet for example.
Clarity (PC/Mac or LX): IP --> 126.96.36.199 Subnet --> 255.0.0.0 (configert via network-settings)
Capture Polar (PC): IP --> 188.8.131.52 Subnet --> 255.0.0.0 (configert via network-settings)
Enttec OED: IP --> 184.108.40.206 Subnet --> 255.0.0.0 (configert via Enttec NMU)
If you run Clarity and Capture on the same PC via Loopback (127.0.0.1), than there is a problem to connect the Enttec OED, but this is not a clarity issue.
In the patch of clarity set the first Universe to Artnet 0 for universe 1.