A radiant wrasse is in the Halichores genus and has more in common with six-line's and leopard wrasses, then Tusks and Lunares. If the radiant is added first, and you get a Tusk south of 7", I doubt he'll even notice the radiant.
That said, longevity of radiants have recently come into question. There are quite a few reports of them living to about a year in captivity, then dying out of the blue. I was planning on, actually the same two, a radiant and Tusk in my 125, before my Tusk died and I changed stocking plans.