The rogue mercs don't have any AR, so I guess I assumed all mercs were ITD as it'd be weird if they just made them ITD and the town guards have to make an AR check. Plus it wouldn't be the first time Blizzard had a column in the MPQ files that turned out to not do anything.
I'd check the basin - as that's where I recall reading a thread that stated that - but it's currently down. It would be easy enough to test, though.
EDIT: Tested with Act II merc in Normal (Level 12 against level 12 zombie with 1000 AC), act II mercs are not ITD. Sorry for the confusion :(
Also checked with an Act I merc. They have no listed AR, yet they don't seem to ignore target defense either. Not really sure how their to-hit is determined then.
I'd check the basin - as that's where I recall reading a thread that stated that - but it's currently down. It would be easy enough to test, though.
EDIT: Tested with Act II merc in Normal (Level 12 against level 12 zombie with 1000 AC), act II mercs are not ITD. Sorry for the confusion :(
Also checked with an Act I merc. They have no listed AR, yet they don't seem to ignore target defense either. Not really sure how their to-hit is determined then.