Arq uses its own format. However, the developer of Arq has provided an open source restore tool on github:

http://sreitshamer.github.com/arq_restore/

http://www.haystacksoftware.com/blog/2010/04/open-source-arq...

Edit: the files on Github have not been updated in 3 months. So this most likely can't restore Glacier backups.