Can White Draw This?

why not 6. a7 rather than Ka7? A promotion would have been unstoppable right? If 6.. Rxa7 then 7. Kxa7
Am I missing something?

actually a better reply for black to 6. a7 would be
6...Kd7 (white can't promote without king support), so 7. Kb7 Rb2+
then if 8. Ka6 or 8. Ka8, black plays 8...Kc7

the best line i see for white with 6. a7 continues with 6...Kd7 7. h4 Rb1+ 8. Kc5 Rc1+ 9. Kb6 Rc8 10. Kb7 at which point I think white might have a draw

Against perfect play the starting position is lost for white.
After 4.Kd8, the game was a draw with perfect play.
See for yourself at:
http://www.k4it.de/index.php?topic=egtb&lang=en