I get your point. First of all the cleric who gave such statement must bring out proof to validate his statement. If he does not provide a agreeable proof then his statement is nothing but a means to provoke an unwanted division or problems in India. Also if Lord Shiva is a messenger of Allah, this message would have been informed in Quran or Hadith's. As far as I recall there is no message quoting this statement. Hence I would say it is Blasphemy.
On the other hand Declaring a five million $ bounty-I would say I am also getting angry hearing that somebody puts out a statement 'Lord Shiva being messenger of Allah' without any tangible proof. However to declare a bounty for such thing is not the right way of reply. It will create a bad impression on Muslims (Which I think was the point of cleric to declare such statement). We must face him through debate that he is wrong. That is the righteous way of reply. The cleric who gave such statement must be ready to debate with Muslim scholars publicly.