You may realize this, but sometimes the obvious gets lost in things. You can upload easily into the GFUI operations space as your scan your primitive vectors. After you have done your scan for the engrave, just upload an SVG of whatever shape you need. It’s another step, but sometimes worth it for getting a good cutout.
I keep a folder full of PDFs of basic shapes (lines, circles, ovals, squares, rectangles, triangles, teardrops, etc.) that I can just drag into the GFUI to add wherever I need them. Now that you can add vector artwork it’s almost as good as having the shapes built in.
When you go back to the catalog view you’ll also find it’s been dropped there for you too (but only the first thing you drag & drop in a session). You can do multiple drag & drops too.