Technically there were about 50 u-boats unaccounted for after WW2, but some have since been discovered as wrecks. It is plausible that there are operational u-boats out there somewhere, but they would be hopelessly obsolete now. There isn't much evidence that they formed any major part of the
ratlines. There was no need. The world at the time was in chaos, and provided you had decently forged papers, nobody much cared who you were or where you were going post-war, as the world was overflowing with refugees. Why take a cramped stinky u-boat cruise when you can sit on a comfortable ocean liner and smoke, eat well, and chat up the girls?
Firstly, there is this article
link, but the DNA was matched against Hitler's living relatives and his dental records for a match. The whole Hitler survival myth is sensationalism, much like the ongoing story of nazi super-scientists creating super weapons that are still current. Unless you seriously believe in the myth of Aryans being supermen with magical powers, there is no reason to believe these other stories.