I could care less about anyone's prior right to the land when it comes to the archaeological record, and neither would most archaeologists. Any solid evidence of Caucasian habitation in North America before 1000 AD would be a monumental find, and covering it up would be as difficult as hiding a Bill Clinton intern affair. If Caucasian remains were found, it would certainly be no justification for any claim of prior possession by European colonists, but the questions that would arise would make for a fascinating exploration.
And a word about who "discovered" America. I have always felt that the term "discovery" used in this sense referred to the revelation and exploration of a new and unknown territory to a civilization that had considered the world pretty clearly defined and known. The Vikings cannot lay firm claim to discovery, because the nature of what they had stumbled on was never understood by them, nor was it communicated within the Pan-European Civilization of the time. To them, Vinland was the last in a string of forlorn outposts that included Greenland (another colony doomed, as Vinland was, to extinction) and Iceland. Nor can any other group, Phoenician, Chinese, Celtic or otherwise, lay claim to discovery in this sense. It may even be probable that many wanderers came upon the North American continent, either through intent or accident. These people either never returned to spread the word, never knew where they had been, or didn't find anything of enough immediate value to attach importance to the place. Regardless, evidence of their would be fascinating from a historical standpoint.
And before anyone jumps on me with both feet for not acknowledging that indigenous people "discovered" America, let me say that they certainly did discover it in the sense of being the first to penetrate and populate it, but not in the sense I have defined above.