Ok well here's a little trick I do to quickly get Vectors from things like logo images etc in Inkscape when I don't want to trace around things.

Import the image then create a new layer and call it something like vectors. Next, select the Fill bounded area's tool, the icon looks like a pouring bucket, and click on the logo or the areas you want to turn into vectors. Set a small fill Stroke something like 0.1mm as it will add this around the area.

Now on your Vector layer when you click on it with the select tool you'll see it says something like "84 nodes in layer vector".
If you turn off the vector layer and use the select tool on layer 1 you'll see it says something like "Image 1050x 1250 embedded in layer 1". This is your original image without vectors which you don't need anymore so now turn the Vector layer back on and turn off Layer1.

Now you can just save this as a DXF and away you go, this will load straight into sheet cam. It's very easy and quick.