There are several things for a modern kitchen. Refrigerator, sink, spice rack, and pots and pans.

I want to take the stove .nif and .dds from Fallout 3 Tranquility Lane and put it in my custom house. Can I do this without fear of penalty? They are both Bethesda games.

For one, game assets cannot just be put from one into another and expect them to work.

Even if you just convert them, its not allowed: http://www.gamesas.com/bgsforums/index.php?showtopic=646586


To use them they would have to be made from scratch again.

Well, there's not going to be any penalty if no one finds out about it - so as long as you don't upload said mod to any sites and you just use it personally, then it won't effect your game or anything.
Oblivion and Fallout 3 are 2 very different games though! Are you sure it would fit in well? Seems like a weird mix of post-apocalyptic world and fantasy magic world to me, but it's your choice.

Good luck!