So here's what happened to us:
Our first nem is a Zebra Stripe, we had bad advice from our LFS that it would host clowns. Except that it has turned out to be a really pretty nem, I love the color on it a lot. But lonely clown fish are lonely clown fish. So I ordered a RBTA from Vivid Aquariums. The zebra is firmly in the sand bed, has been there for almost a year now, so I hoped that a RBTA would pick a spot on rock and the two would be ok in the same tank.
The day after I ordered the RBTA, my female clown moved into the old nem. I thought there was disaster coming for sure except they seem to have made an arrangement and both seem happy. (The male clown is not at all sure about the situation.)
The RBTA arrived and is absolutely gorgeous (and huge!). I put it into the tank and after a couple of hours attached pretty high up on the rock and in pretty decent flow it climbed behind the rocks and has been in hiding for four days. I'm waiting to see how all of this is going to play out.