Just an update on how this all turned out.
I got a post-2001 9-Speed Mirage RD on E-Bay for around $30. When I hooked it up and tried adjusting it, it would skip a gear when shifting in the smaller cogs. If I got those adjusted so they shifted smoothly, the bigger cogs wouldn't shift smoothly.
I dropped it off at the LBS hoping they could tune it up. I got a call from their mechanic the same evening and they said I needed a 8-speed derailleur since my shifters were 8-speed. I knew this might be an issue, and I read that the JTek Shiftmate Model #1 might solve the problem with different cable pull ratios between older shifters and newer derailleurs. (I contacted Jtek and was told Model #1 might work). So I ordered one in case the LBS couldn't get things to work.
The next day, I got another call from the LBS saying that the problem was my barrel adjusters were broken - (this is a 1996 bike). I was skeptical because I was certain the problem was mixing an old campy shifter with a new campy derailleur. But I had them go ahead and change all the old cables and housing.
Well, lo and behold, that did the trick and now everything shifts smoothly in all gear combinations!!!
So there you have it: Pre-2001 Campy Mirage 8-speed Ergoshifters WORK with Post-2001 Campy Mirage 9-speed rear derailleurs assuming all cables, housings, barrel adjusters are in good working order.