Assuming that you're not talking about download accelerators, there are some web accelerators that work differently than what Mak213 explained. Those accelerators mainly do 2 things.
1. They have a way to more intelligently cache images and website data onto your local hard drive. So the first time you load a page it's normal speed, but from then on, it loads the pages from your hard drive, which gives you speed increases. The software is supposed to recognize when a page has changed and only download the changed part. In my experience, it doesn't work and you never see the changes. It just keeps loading the same data from your hard drive over and over. It's horrible for dynamic pages like news and weather reports, or pretty much anything else.
2. The software looks at all of the links on a page and starts pre-fetching the info from those pages because it thinks you might click those links. So when you actually click one, it has already loaded part of the page. This is also ridiculous because it unnecessarily wastes a lot of bandwidth.
These web accelerators are worthless. At first, it appears that you are getting major speed boosts, but it doesn't take long to see through the facade and realize the huge flaws. But to answer your question, yes you can use them with DSL, but they're worthless, and the difference won't be very noticeable with DSL anyway.