My Silhouette likes dxf files, which I draw in Autocad but a less expensive drafting program should be able to output that type of file. I'm using version X6 for Corel Draw and it doesn't work for me. The newer versions than X6 are not likely to handle them well either, but I don't know. The Silhouette software is hard for me to work with but that may be because once I made dxf files from Autocad work there was no point in going further.
CorelDraw is great for drawing decals because it handles colors far better than AutoCad.