The more important question than 'Is it legal?' is whether or not Blizzard will remove your map. Since Blizzard technically owns all maps created with the editor, they could be held responsible if their 'property' breaches copyright laws. Litigation in these cases rarely occurs. The more likely result is that Blizzard would remove your map 'just in case.'
As stated elsewhere in the thread, though, your map would have to be reported first. DMCA laws in the US often cause companies to act in a 'remove first, ask questions' later policy, but if you look at the custom map list on Battle.net, it seems Blizzard is allowing many maps violating at least trademarked names.
It should be mentioned, though, that Music copyright has been a hotbed of litigation in the past few years, so I would suggest you avoid using copyrighted songs. Last thing you need is the RIAA dropping a 50,000 dollar fine on your ass, PER SONG.