I was curious because it says you have to guarantee the booking using amex card:
Cardmember is required to book in advance by calling Taj Reservation Worldwide or via www.tajhotels.com ,www.Seleqtionshotels.com , www.vivantahotels.com or email at reservations@ihcltata.com. At the time of makingthe reservation, the Cardmember will need to guarantee the booking amount by using the American Express® CreditCard as applicable
They do not ask for any card details, I've used the vouchers 2 times. They adjusted the voucher against the bill and the remaining amount I've paid using HDFC TATA NEU card. The reservation front office do not care from where we got the vouchers, it should be Stay/Experiences vouchers that's it.
You can still call the Taj Central Reservation office and ask them if the card is required when redeeming the voucher or not.