Regarding, "お目付け役 (Ōmetsuke-yaku)", I feel that "Officer", "Enforcer", "Agent", or perhaps even "Investigator" would be appropriate. Some google digging turned up this: http://en.wikipedia.org/wiki/Metsuke

It seems the ōmetsuke were essentially the top level of internal affairs intelligence officers within the Shogunate, focused on monitoring the activities of daimyō and government officials and then reporting directly to the rōjū/elders (top government officials during the Edo period/Tokugawa Shogunate--effectively the Shogun's "cabinet" or high council).

Most relevant bits: "...the ōmetsuke, were responsible for supervising the activities of officials and members of the daimyō (feudal lords)." & "The ōmetsuke reported directly to the four or five rōjū at the top of the shogunate bureaucracy." But considering that his name translates to "Station Master", I'd lean towards "Officer" for the personality translation.

Also, "-yaku" ( http://eudict.com/?lang=japeng&word=yaku ), in this context, seems to imply that the preceding term/title is a role or position being filled/performed. Sorry how long I rambled, but it got fascinating once I started researching the phrase.

TL;DR: I think "ōmetsuke-yaku" should be translated as "Officer" or "Enforcer". Thanks!