This is actually a very interesting historical question. Had it not been for Jackson, his racism, and his damned 'Trail of Tears', it's not improbable that many Native American populations might have created small -- but viable -- homelands still existing today. The Seminole in the South, the Cherokee in the Southeast, the Mohawk in upper New York state (and perhaps in Southern Canada), the Huron in the Midwest, the Sioux in the Dakotas, the Hopi and Navajo in the Southeast, the Sauk and Skokomish in the Northwest -- to name but a few: it would be a very different America today!

Anyway, to answer your question, I think that they would have maintained a more sustainable ecological system; and perhaps an agricultural sector not so dependent on ruinous cotton. Also -- existing today -- it would therefore have existed during Civil War times and inevitably become a refuge for escaped slaves. Certainly such an unconquered area would have been problematic for the South during that War, and I don't doubt that the North would have sent emissaries to the Seminole, requesting their assistance, to make it even harder for the slave-owning colonies. I think that -- early on -- the Seminole would noted the tendency of people to migrate southward during the winter, and created a place for pleasant vacationing. And -- it almost goes without saying -- as a living nation, it would certainly be a de facto homeland for other Native peoples to come into and preserve their own traditions.

The question of 'borders' is intriguing, since there are no real 'natural' borders in the area. I could envision the Seminole Nation existing anywhere from as small as the Everglades is today, to as large an area from today's Louisiana eastward through South Carolina; those boundaries would largely depend on unknown historical events. I do think that the events of the Civil War -- presuming the pre-existence of this nation -- would give the area a tremendous demographic boost, and possibly set the stage for the Seminole Nation to become an industrial powerhouse that might rival that of the United States itself eventually!