Most of the platforms that Cadillac is using are European. The STS and CTS are on an Opel platform, the SRX is on another Opel platform, the XLR is a Corvette, and the DTS (lumbering FWD barge with diminishing sales) is on a domestic FWD chassis, and it *shows*.
"Which models in the current Cadillac line are designed in Europe?"
As the new CTS was being developed, GM made a big deal to show it being tested in Germany. After it was introduced, they continued to highlight the European input for it.
Now GM has indicated it will try to sell Cadillacs in Europe.
The Catera of a few years ago was simply a "badged" Opel from Germany.