The best way to tell is to read the magazine from that publisher from issues of the preceeding year to tell the type of story they want.
As long as you send a story that could be categorized as something an editor wants (some editors may call it "dark fantasy" while others may call it "supernatural horror"), you can send it to those editors. "Close" counts in horseshoes and in submissions, most of the time.
Dark Fantasy may include elements of the supernatural, but I would say it's primary focus is fantasy. (Clear as mud, right?)
See this pic for 1000 words of Dark Fantasy.
http://1.bp.blogspot.com/_7mdcmbs3CVQ/SmcLpaeSL-I/AAAAAAAAADQ/Hd9QlNZLAws/s1600-h/The-Dark-Is-Rising.jpg
See this pic for 1000 words of Supernatural Horror.
http://www.matthewhunt.com/blog/images/dragmetohell.jpg
Axe
Some stories are hard to classify and there are a couple of markets that say they want those too. Or that cross genres.
Other than that, from what I have heard from a couple of pro editors go with what Kathleen said.
As long as you don't send SF to a Fantasy market or Horror to romance etc.. all they will do is say no. If it's close they may just like it.
Anna
You could try doing that reading at ralan.com or Duotrope's Digest duotrope.com.
I like the way things are listed better at ralan...its easier to find and to understand but evidently many here like the other one because you can check on how well they do at sending rejections and list your submissions somehow. Come to think of it I think ralan does the rejection thing too but I usually don't use it.