It depends. If it's hardware raid then DBAN will only see one drive and wipe it without any problems
if it's software raid it gets tricky because when you boot from DBAN CD, the OS where the software raid is installed does not start - therefor I don't know how DBAN will see your disks.
My advice, if you have hardware raid do it because you won't have problems - if not than wipe each hard drive individually for 100% guaranteed that you done it right.