I have never heard of any restrictions in Silverton on taking photos, and the entire D&S property is unfenced and accessible to anyone. I've taken pictures in Silverton for 49 years with never a problem, and I think everyone associated with the D&S is quite agreeable with photo taking. It is some of the best advertising they could ask for.
The fiasco with the picture concession prior management tried to cram down Silverton's throat concerned pictures of people in front of the engine while parked at the end of track and that track is in the public right-of-way. That proposal and the related strong-arm tactics of the one season general manager led to Al Harper taking control of the railroad and that resulted in a very positive response to the public that continues to this day. Take all the pictures you want in Silverton.
There are some right-of-way restrictions, like the high line, and climbing the fence in Durango, but those are based on safety issues and control of the shop area and realted facilities from light fingered visitors.