Dear Mr. Paresh Jain,
I feel that My Learned brother Razesh Ji has misunderstood your query insofar as he has gone to discuss the issue of a GTA itself. As per available info, it seems clear that your client is a service recipient and you want to know about availability of Cenvat Credit of tax paid by him on the GTA input service.
For this I would opine to the best of my limited knowledge, that the Cenvat Credit is very much available to your client but he cannot utilize the same in paying the tax on GTA Input service. As per law, the tax under reverse charge mechanism (such as GTA, foreign commission etc.) has to be paid in terms of money only and not by credit.
Off late there have been some judgments to the contrary which actually allow utilization of credit of GTA to pay tax on GTA itself later on, but I would not suggest the same to you.