Yes, the GF software in the “cloud” interprets a filled, closed path with no stroke as defining an area to be engraved. And since engraving is done as a raster, the process basically rasterizes it.
If you want a donut, you make a compound path from two paths – the path defining the hole inside the path defining the donut. The result is a shape that’s “painted” where the donut is, but not where the hole is. This will show up in the GFUI as a single operation that raster-engraves a donut.
If instead you tried to make a donut by stacking a white-filled path representing the hole on top of a bigger filled path representing the donut, it wouldn’t work. Doing it that way defines two areas that the GF will interpret as places to be engraved. One shaped like the whole donut, including the hole and the other shaped like the hole by itself.
To the GF, white is just another color, so what you’ll see in the GFUI is two engrave operations (because there are two colors – donut-colored and white). The first operation will engrave the whole donut, including where the hole should be, and the second will engrave the hole a second time.
Hope that helps make sense of this confusing topic.