Brazil’s tax watchdog opened a probe on whether about a dozen people involved in the Petrobras corruption scandal also allegedly had undeclared accounts with HSBC Holdings Plc’s private bank in Switzerland, two sources with knowledge of the situation said on Saturday. A former manager at the state-controlled oil giant Petróleo Brasileiro SA had an account at HSBC’s private Swiss bank, said the first source, who requested anonymity since the probe has not been made public.