I had a success rate of only 1 in 5 with an oreiad vs. blood henge druids when I tried this. Becomes quite expensive use of the oreiad at that rate (though I did get a big armor in the process).
I think VFB had a very lucky run. My testing with the Oreiads is pretty consistent with what the rest have said. I normally equip them with the knowledge that they are going to be seduction failing assassins. Next time they should use the hot chicks as seductresses imo.