NG doesn't need any German company to help them design and build subs. They have Newport News Shipbuilding -- currently building Virginia-class boats.
While I can understand buying the German design to conserve stretched-out engineering resources here in the US, I don't understand why NG would buy a German design, then turn around and have the boats built in Taiwan. What's in it for them?
Newport does not currently build any diesel subs. Buying the design from the Germans makes sense.
Last time I checked Northorp and Grumman were still primarily aircraft designers. True, they operate Newport News Shipbuilding Co., but that is a manufacturer of Nuke Boats. Their expertise wouldn't get them much past the hull design since there hasn't been a suitable diesel-electric system since the '50's here in the US.
The major cost of new weapons systems is the design work. That is why there was so much todo about the Army scrapping the Crusader Artillery System -- the design was already paid.
Besides, conventional boats don't have unlimited power generation capacity. They must therefore have smaller displacement, crew size -- everything. You can't just take the hull plan of a Nuke and slap a diesel-electric plant in it. Just imagine trying to mount a snorkel in the Conning tower layout.