If I have a tool that's sparking and there is dust collection, the tool is not a wood and metal and wood and metal tool, it's metal only.
I don't sand much woodworking, so my sanders are for metal work only. The run of hose that the sparks go through doesn't mix metal and dust. That's extremely unsafe - especially if there's a chance of both going through at the same time.
I just ground some bolsters on chisels with a purple belt that runs 4800 feet per minute (36 grit). The spark coming off is so coarse that it was landing on my feet (not wearing socks) and I could feel it burning and smell it burning. I moved my feet. If those sparks were going into a machine that had wood dust, there's almost no chance they wouldn't create smoke at a minimum. Even when they hit each other where a pile of swarf collects, they fuse to each other a little bit.
I hadn't thought that much about the cyclone until this came up - the reason I'm using it (and there *is* wood dust in the barrel below it), is because I don't want all of the black dust going straight through to the shop vac and clogging it right away. The small dust deputy that's no good for anything more than a sander is excellent for metal dust - it'll swirl the spark around that goes through a 10 foot hose for a while before it's allowed to either drop into the can or the little bit of it that makes it's way past and gets to the vacuum.
I can say for sure also that a flat belt that I have that runs only 2200 feet per minute will literally allow the spark to burn the plywood table that the machine is on, so I leave a cushion of metal swarf under the bottom of the belt where the spark is directed - otherwise the ply table top will capture spark and a ribbon of smoke is the result (stinky).
The way I'm doing things is safe. using a dust capture system on the same tools that I have with wood dust around the machines or in line somewhere, definitely not.
Worked at a cabinet factory when I was in college, and the year before I'd gotten there, someone swept screws into one of the capture points and it started a fire as it sparked through the metal dust lines with the wood dust coming through at the same time. Bad situation.