Many Russian (possibly other nationalities as well) Jews named Chaim (or Chayim or any of the other variations) immigrating to English-speaking countries changed their name to Chyman, thinking that that was how their name would be construed there, or that it would help them assimilate because of other names ending in -man. This is what my great-grandfather did when he came to England.
Does he have sisters named Virginia and Chastity? I know that this is just a name information site and that nobody is encouraging names... but did people know what a hymen was back in the day? And I hope that he doesn't provoke any fights, otherwise someone will try to "pop" Hyman.