I'm no worm expert but , yes, the "snake swimmers" are what I call detritus worms. But what matters to me is that they seem to be one of the larger type things and we can see them but they don't seem to do much harm. I only see them when I've moved some plants , etc. so I have to assume they are there more often than I see them and my fish are always picking around. I have to assume they are trying things. Sometimes it is good to eat and other times it winds up like the times when fish try to eat the freckle on my arm! I tend to be a bit on the "low worry" route, so if I can let nature take care of cleaning or controlling the worms, I'm okay with that. Not fully into doing it "natural" but then I'm also a long way from wanting to worry issues that will lie dormant if I don't bother them?
If I get sick/unhealthy fish or plants, then I do something but if it is only seeing something weird like worms, I may ask but do nothing.