.dat files contain the parts of the actual 3d model, (hull, cranes, funnel, vents, lifeboats, etc.), and the locations of each of these parts. It also contains the locations of non-3d node points, such as sound files' originating points, flags, and cargo. Most other details are included in other files (damage models are in the .zon, for example).
Also, most .dat's actually do not contain the actual texture (i.e. multiple skin ships). Of the ships which have embedded single textures, Sergbuto fixed the C3 and many of the destroyers, and UBOAT234 recently fixed all of the rest (even the four coastal crafts). You probably already know some of that though.
EDIT - And no, I don't mind having my ships included in free mod packs - I like to see other players enjoying them.