While the Hitler Jugend t-shirt might not be entirely accurate aboard an U-boat, t-shirts of similar design actually existed:
http://www.warrelics.eu/forum/hitler...od-fake-23312/
http://www.warrelics.eu/forum/hitler...-shirt-297073/
http://www.warrelics.eu/forum/hitler...em-shirt-6140/
From pictures I have seen, I don't think that the Kriegsmarine dressing code was strictly enforced aboard U-boats; I imagine that no captain would have complained if, in the closedness of his galley, a nazi fanatic cook had decided to wear an HJ t-shirt he had got who knows how/where.
That said, the KM shirt you want to use in place of the HJ one, is much more plausible, and from a
drawing I have found, it might have been part of the "standard" U-boat clothing.
What I don't get about your questions is: you have already posted the texture you want to edit/replace and its name, which other texture are you looking for and, besides that, I don't see how the editing of a dds file might cause a black screen
