Sorry, can't help with the poem, but I think, I can throw some light on
this question. In long gone days, there was a letter in Telugu which had
similar pronunciation to the Tamil 'zh'. This letter was found in some
stone inscriptions ( I read this in some book, which I forgot). It was
discontinued later, and I am not sure if it degenerated into the present
day 'sha' or 'ya'. It is not connected with 'banDi ra', and definitely not
with 'aloo' which is a vowel. If you notice, all the Tamil words in which
'zh' occurs are pure Tamil words, i.e. not borrowed from other languages,
including the name of the language itself (it should be 'tamizh'!)
Tamil also has a special 'ra' which corresponds to telugu 'banDi ra',
though you do not find much difference in the pronunciation.
Hope this helps.
Nasy