Could anyone tell me if this site is legal or not?

Just my opinion but I would say it is because they are remixing the tunes rather than simply ripping them. Though I suppose if the original was nay then any modification would be aswell.
If they're still there I recommend Gunbound, Sonic2: Chemical Zone and the rock remix of that.. valley in Zelda64.. can't quite remember the name :( .

- Mike