I came across an intriguing bit of information on Marcus Piso in the book, In Search of Paul (p 55), by John Dominic Crossan.
"In his 'Jewish Antiquities', Josephus preserves a long list of official letters once in the hands of various local Jewish diaspora communities that document Rome's toleration and support of their practices and traditions. Among them are two belonging to the Jews at Delos. In the first one, written in May or June of 49 B.C.E., the Delians proclaim - apparently begrudgingly - that they will obey the Roman legate Marcus Piso by exempting Jewish citizens of Delos from military service:
"Decree of the Dleians. 'In the archonship of Boeotus, on the twentieth day of the month of Thargelion [May/June], response of the magistrates. The legate Marcus Piso, when resident in our city, having been placed in charge of the recruiting of soldiers, summoned us and a considerable number of citizens, and ordered that if there were any Jews who were Roman citizens, no one should bother them about miltary service, inasmuch as the consul Lucius Cornelius Lentulus had exempted the Jews from military service in consideration of their religious scruples. We must therefore obey the magistrate.' (14.231-32)"
It appears to me that Jews of Delos were given preferrential treatment because of the influcence of the Jewish sympathizer Marcus Piso, and that Marcus Piso was himself probably a Herodian in Roman clothing.
© Charles N. Pope, US Library of Congress. All rights reserved.