Earlier quoted context omitted.
See eg https://github.com/mattdesl/parametric-curves/ and https://developer.nvidia.com/gpugems/gpugems3/part-iv-image-... You can builds all kinds on top of pixels and triangles.
That's like saying "GPUs support Master Chief". You can model Master Chief with triangles, and you can model parametric curves with triangles. But I wouldn't call it "supporting parametric curves", you're still rasterizing triangles, they're just morphed into the shape of a curve. And most practical, shipping versions of this technique would do adaptive triangulation on the CPU, since otherwise you don't have an idea…
The parametric curves don't get transformed into triangles. This isn't tessellation or similar techniques. You aren't feeding the GPU any triangles - you're only feeding it the function that defines the parametric curve. Then, using that function for the parametric curve the GPU can calculate pixel output. Again, modern GPUs (really, most GPUs in the past decade) can support more than just triangles. These more exotic techniques don't get as much attention, since most graphics assets are still implemented with triangle meshes.