The German Showline dogs can certainly do schutzhund- there's one at the club I'm going to that's doing very well. I wouldn't call them the best line of dog for the work, nothing you'd see at a national level, but for club level, yes. Absolutely.
I'm not sure of this particular line, as I'm not very well versed on the showlines, but going strictly on the pedigree... I'd say these dogs look good. Lots of V and VA ratings (which basically means "good" and "very good" for German show dogs).
I'd definitely call the breeders, though, and get a dialog going. Always best to know your breeder, even if its just through phone conversations/emails.
GSDs- Mulder, Ridley, Vega
GSD on the half shell- Rigel