Dear Paolo,

I have seen a paper (maybe it has not been published yet) by Ilona Kedzie; email: ilkedzia@gmail.com) about a Tamil siddha who actually visited colleagues in the moslim world. But maybe you are only interested in 

traffic into the other direction.

You might also be interested to read her article "Global Trajectories of a Local Lore: Some Remarks about Medico-Alchemical Literature of the two Tamil Siddha Cosmopolities" in Cracow Indological Studies 18 (2016), pp. 93-118. If you don't know the article already.

Best, Herman