Tried it out, it is quite the MF'er.
I differentiated on the merc's ideal equipment.
It doesn't seem logical to mass up half a dozen MR just to get the ideal merc. set up. As you can get the same set up with half the MR required. The hook? Socketing rare jewels into unique armor with open sockets available.
Below you is my merc's set up.
ETH Kelpie Snare (acquired around Lv56 NM mephisto)
Up'ed ETH Kelpie Snare (Up'ed around Lv72)
Up'ed ETH Kelpie Snare + Ber (20% CB + 75% Slow) (Socketed around 84,trading 3 MR for the Ber)
ETH Black Hades Armor (9oo+ Def + 248AR/60DMG%+ to Demons + 3OS) (acquired in Normal Baal Lv 47) + Rare Jewel(49AR/40DMG% to Demons + 7% FHR) (acquired around 67 NM Baal) + Rare Jewel(15Res to all + 7%FHR) (acquired around 65 NM Baal) + Shael (acquired through NM countess) Didn't upgraded armor*
Possibly turns to...
Up'ed ETH Black Hades Armor (17oo+ Def + 248AR/60DMG%+ to Demons + 3 OS) + Rare Jewel(44AR/40DMG%+ to Demons +7%+ -15%Req) + Rare Jewel(15Res to all + -15%Req ) + Shael
Black Horn (acquired around level 55 NM Mephisto)
ETH Vampire Gaze (acquired around level 73 NM Baal)
UP'ed ETH Vampire Gaze + PDiamond (Uped and socketed around level 78)