If by nutrients, you mean acids, hormones and such, then yes, I'm sure most plants contribute acids and other chemicals to the soil (probably different ones from different plants), which will affect different plants in different ways. Different plants may attract different kinds of microbes, and animals, which may also affect the soil nutrients (different ways for different kinds).
Different acids and other chemicals have different effects on different things. Whether it's an improvement (and what it's an improvement for) depends, but it can be an improvement, I believe. Different acids may make different elements more or less available to different plants.
If by nutrients, you mean elements, that's another matter that other people seem to have attempted to answer, with the discussion on nitrogen-fixing. Legumes tend to have microbes that fix the nitrogen (the plants themselves don't actually do it). Some other plants, I've read, can hinder this process (such as calendula, I believe), and may not be good to plant with legumes.
I suppose a venus fly trap may catch insects, and their left-over skeletons may eventually somehow contribute to the soil.
Trees can grow deep roots to bring nutrients from way down to the surface (the trees drop their leaves, which contain nutrients from down below, which may be able to contribute to the topsoil in ways).
Because many plants have delicious fruit, they influence humans to grow them, and the humans may improve the soil as a result (as well as the plant breeding; so, it's a synergistic effect). It's kind of like a symbiotic relationship, except humans aren't actually attached to the plants.
I suggest learning about cover crops. There's more to good soil than fertility (like soil structure, and probably more stuff). Buckwheat is supposed to be a good one (but not for nitrogen fixing).
In short, the answer is yes. People usually call them cover crops if they're planting them specifically for the purpose of improving soil.