No, it's not the same technology. The ES3, if I am right, should be 2-drivers and uses the older technology. Something like Westone 3 Custom will eventually come out, and it will be interesting to read impressions about those.
"The ES3 is the world's first true three-way, custom in-ear musicians' monitor."
... which sounds to me like it's a triple driver. I think the ES2 is the 2 driver version, on which the UM2 is based, so I assumed that the Westone 3 is based on the ES3.
I'd love to know if Westone are working on developing their custom IEM range as well - if money was no object I've always thought that I'd go for Westone's customs rather than UEs, even if they don't get the same amount of interest - I love the Westone sound.