I've tried playing with Magick++ and drawing few simple primitives:

Magick::InitializeMagick(nullptr);
Image image(Geometry(1900,1200), Color("white"));
image.strokeColor("red");
image.strokeWidth(10);
image.draw(DrawableCircle(100,100,50,100));
image.draw(DrawableRectangle(200,200,270,170));
image.write("test.eps");

And those primitives do not seem to be vectorized. Checking the .eps file in notepad shows, that after prolog it uses DisplayImage procedure, but doesn't contain primitives. I know ImageMagick supports reading postscript, but does it support saving to it with actual vectorized primitives, or does it do some type of conversion to an image which is not vectorized at all? Couldn't find information about this anywhere.