I think he's pure arab. More of a traditional arab than the new showy arabs, though. He looks a lot like my friend's eqyptian/polish arab cross. He doesn't have the extreme dished face like you see today, but the extent of what you see now is generally bred into them-much like the height has been to warmblood breeds. I know Hanoverians were originally bred for the German cavalry and as cart horses.
I've seen many arabs that just have all of their flee bitten spots concentrated into one area-which is what his splotchy areas look like. Sometimes instead or in addition to having flee bitten spots all over their body, they will accumulate in different spots, from what I've seen they tend to be on shoulders most often.