Indeed, they chose to use the second opening for FMA on top of the first opening video. Ready Steady Go is a good song, (YAY L'ARC!) but it's definitely really strange, since the coordination must be allll off.
I really have to wonder what they're going to do with the other two different themes for the opening. O_o() Will they keep it, or still play Ready Steady Go over them? ...The song will really not fit the last intro's images.
The group that sang the intro (L'Arc en Ciel) is a pretty big hit in Japan, and they're just breaking through in the US. The decision to have their song as the intro all the way through must be great for them.

(All the same, though, go find the other intro songs; they're great too.)