Like Dan said, nothing wrong with keeping a topic open. This is only reply #21 but the topic has had 140 views, so others are reading and learning, which is what this is all about.
As far as the dowels to hang the sausages from, you should have no issues with aluminum, steel, etc for this application. Metal rods will get hot though. Not a problem for these summer sausages hung by string, but other snack sticks and such using natural casings or collagen can break as the casing in contact with the metal rod dries out and weakens. Hickory dowel rods from any hardware store are a good option, at least 1/2" diameter for stiffness.
Try to keep a little space between your hanging sausages for better flow of smoke color, not so much for flavor, and this too is less important for fibrous casings (that will be peeled off anyway) than for natural casing sausages.