Just watched Loups=Garous and the band feature quite a bit in it.
Music wise you probably are already aware that Midnight Television is the opening theme and Sayonara My Friend closes the film - but Koshi-Tantan is also used as an insert song complete with an Animated video of the girls! And as a subtle bonus, one of the main characters, Mio, is a big SCANDAL fan who is seen wearing some of their different uniforms throughout the film. She also has a Kanta backpack and another piece of unique Kanta memorabilia that I won't spoil for you. 
Having said that this is not really a SCANDAL film so if you are going to watch it just for them you maybe disappointed, but Anime fans should enjoy it as a piece of work on its own merits (especially since it's from Production IG).
I heard that the girls were also involved in some VA work for the movie, too. My guess is that they were in there towards the end; I think I half hear Rina, but she said (maybe in the navigation disc?) that it was quite difficult because she had to keep doing retakes because of her accent; they wanted a non-regional accent. Or I could be imagining things. I do like the movie, though. It's actually really interesting, but here's not the place.
I just saw this on Youtube and been wondering if there are HQ versions of this available for download...
This is from the Navigation Disc, and it's like the first part of the SCANDAL meets Loups-Garous clip, and they show the making of the clip (which is hilarious when you think about it when watching the PV!). I have the file, but I don't know how to cut it, and the whole clip is already on the thread somewhere.