Fallout wiki has photographs of the cards and poker chips from the collector's edition. Would it be legal to use these photos to texture items in a mod?

I don't see why it would be. They dont really own the photo's of the items. Its like saying 'Would it be illegal if I took a photo of a Ford Mustang and used it to texture a model of the car?' I do not believe so.

The photos of the items were licensed to wikia under a creative commons license. The owner of the physical objects presumably gave permission for the photographs to be taken. The only stumbling block would be the right to reproduce depictions of the artwork that is present on the physical object. Wikia claims this right as fair use for commentary and criticism. The remaining question is whether use in a mod would constitute fair use. It would not fit any of the "preamble purposes" of fair use, but that list is not meant to be exhaustive. It would meet the criteria of noncommerciality, transformative / non-supplanting purpose, small ratio to the total work excerpted, and positive effect on the marketability of the original.

If you're using the pictures as a base to create your own textures, and not altering the actual DLC textures to redistribute them, there's no legal problem. A 10% difference is all that is required. If you created a texture that was more than 90% identical, then chances are you copied it to begin with.

*Nods*

I would think that you can probably use the texture however you want to be honest since the original art for the cards probably belongs to Bethesda/Oblivion.

Is there a DLC that has in-game versions of cards and chips for Silver Rush, Bison Steve, and Vault 21? I'm talking about photographs of physical objects that came in the collector's edition.

I agree.

It's not like you're selling the textures or anything. That might be a whole different story...