Hi,
The Dremel is a great tool for hogging out wood for the tumbler, bridle, and sear from the lock mortise, routing mortises for trigger guard lugs, routing the trigger slot in the wood, cleaning up brass parts, polishing metal, accurately marking holes in metal to be drilled, and many other small tasks. To say it should never be used when gun making is rubbish. Like any tool, you simply have to know how and when to use it.
dave