CSR,
I too think so. The scale S R1 M1 P D1 implies Karnataka suddha saveri (or Gunkali in hindustani terminology). But the song
is very classical, so can't just say scale based I think.
Related raga is the 4-notes only Lavangi (S R1 M D1) - yet another beautiful BMK creation. I recently read in Raj's blog that IR has
tuned a song (below) in this raga ( or rather raga mixture). It was a pleasant surprise to me.
http://www.youtube.com/watch?v=zYo8cB8aM-w
However, this one is just scale based. (To appreciate the raga's real beauty, youtube for it. There's one detailed rama varma rendition.)