Under no circumstances would I use my rear wiper if my rear window was even close to being as dirty as that Rebecca.
Guaranteed scratched rear glass ( although I'm sure you'd buff them out with your trusty DA 
)
Using your car regularly I find its no too difficult to get the rear filthy like that in the curent weather until it gets its clean.
I have no qualms using the rear wipe/wash which gives plenty of wash fluid onto the rear screen as part of the wipe if you use the full on push of the stalk.
Have had no issues of scratched rear glass myself & probably a bit OCD when it comes to such matters.
