As long as the backup drive is larger than the source drive, I don't foresee a problem. Just beware that the WD Green drives have had prior problems in RAID setups by dropping off of the host controller due to the power management algorithms. I haven't heard of any cases recently, so it may have been an initial firmware issue.
I run two Raptor 150-X's in RAID 0 on my main desktop, but I use a Windows Home Server system and BluRay discs for my backup solution (WHS is short term, BluRay long term).
But what you're asking about is what RAID 0+1 is mainly about, so as long as you watch what you're doing when you modify the array, it should be fine.