No, not required. Till recently, PIS Bank account was mandatory for NRE and NRO account and this is not required now for NRO accounts as RBI has scrapped it recently.
To understand better, let's first understand the process involved in settling a NRI trade. Whenever, a NRI client trades, the transaction will first be reported to RBI. It will next be scrutinized for tax obligations, in case of sale transaction, and then be settled. For eg., if you buy 100 HCL tech at Rupees 850, the transaction will first be reported to RBI, your PIS bank account will then be debited for Rupees 85000 + charges. When you sell these 100 shares at Rupees 950 each, the transaction will first be reported to RBI, then scrutinized for tax obligation. In this case it is a profit of 100x100 for which tax will be deducted and then the sale proceeds (after deducting the tax obligation) will be credited to the PIS account. Thus the purpose of this account is to route all purchase and sale obligations arising out of buying and selling shares in the secondary market and reporting them to RBI.
RBI has now relaxed these procedures for NRO mode of trade. Under the new process NRO transactions need not be reported to RBI and hence, thetrades executed in Non Repatriable mode need not be routed through PIS account. The transaction will however continue to be under scrutiny for tax obligations and taxes if any are to be paid before the sale proceeds gets credited to the account. This process is now done by Tradeplus at 0 cost. Hence, PIS bank account is not required any more to executed transactions in NRO mode.