Hi, I don’t know about ON1 Raw and I am actually not that experienced with the DNG editing process.
I think the original poster is trying to get by without Lightroom in any reasonable way.
I think he can use something like the free darktable to export the DNG to another format.
I was thinking that he could try and use the standalone stitcher instead of PTGui (which is good, but may be expensive) in the workflow. The three free pieces of software he would need are: