I have not tried two computers with one EtD, but today without thinking about it I had two computers with two EtDs on the network simultaneously. I was trying to test some dumb strings in my basement workshop using my backup EtD and the show computer with the production EtD was still on the network upstairs - no show running. I would turn on one channel and it would come on and immeadiately go off. turn on a different channel and it would come on and then go off. Finally I woke up, went upstairs and powereed down the production EtD and all my tests in the workshop worked great. So two EtDs on the same universe with two computers connected does not work.
I am not using LSP, but Vixen and xlights.
On another note, it makes me glad that I still have two USB dongles, so I can use them for testing without conflicting with the production system. I have 1 USB DMX and 1 USB Pixelnet. So for folks who say don;t buy a USB dongle I think they are totally wrong. They have a very good use even after converting over to EtD fpr the show. Without them testing duriing a show season becomes more complicated than it needs to be.