The DGX300 if find has too many steps to go through to do anything. But to anwer your question, yes is does save as SMF0 files.
I would suggest that you read the manual for it that can be downloaded at this link:
http://www.yamaha.com/yamahavgn/CDA/ContentDetail/ModelSeriesDetail/0,6373,CNTID%3D2711%26CTID%3D205200%26VNM%3DLIVE%26AFLG%3DY%26LGFL%3DN,00.html