No, not all new replacement radiators are aluminum. I got a nice copper one just recently for my '94 Caprice 9c1.
New antifreeze (green or red) is just fine for aluminum. A lot of engines are made of aluminum either whole or in part, so it has to be.
Aluminum actually transfers heat better than copper if I'm not mistaken. Pretty good conductor, and not very corrosion prone. The problem with those radiators are the plastic end tanks, and the how they are attached. It tends to crack and leak, just like you experienced. So it'll be fine, just won't last quite as long as a better one.
Harry