IF you intend to charge for your game, then you should really get the full DarkMATTER package to be on the safe side. The media from DarkMATTER will match each other, it's a very bad idea to use a few models from here, a few models from there - esp if you don't intend to retexture them yourself, it can make even the most brilliant game seem disjointed and awkward.
If it's freeware, then there's not really that much anyone can do - and TGC don't expect royalty cheques from freeware titles.
As with most media packs, paying for the package entitles you to use the pack in your own creations, but not re-sell them or distribute them yourself except as part of your creation. I think that the same rules apply, they were gifts, so your in the same position as if you'd bought them.
Van-B
Muhahahahaha.