No. As of 11/15/2010, we burn only single layer DVD-5 4.7GB DVDs
You can use a dvd copy software like DVD Cloner to
1) Split your DVD-9 (dual layer DVD) into two DVD-5 (single layer DVD)s. You can then make a 2 dvd set on our site. This saves you trouble of re-authoring your DVD
2) Compress your DVD-9 so it fits on a DVD-5 single layer DVD. The DVD Cloner software allows you to choose the compression levels, and remove any extra features you may not want or need. Compression does affect the video quality, so the final product is not exactly like your original. Depending on the circumstance, this may be acceptable to you.
The reason burn on demand fulfillment companies do not use dual layer discs is because they are prone to error. If you really need your DVD-9 dual layer DVD disc replicated exactly, you need to search for a "dvd replicator". Normally you would have to purchase 1000 units or more to make this cost effective (probably get the price down to $1.75 per unit that way).
duel, dual, layer