Iron will and negative pass-effects. Loophole?
You're correct.

However, Iron Will's second part will still trigger and cause a loss of morale if the check is 0 or less (e.g. if you Jury Rigged on a 7 check and get 0).

Iron Will doesn't make you pass. It just stops the labelled fail effect from triggering. It isn't a loophole in general; sometimes you miss out on good stuff on the pass, occasionally you can avoid bad stuff on the pass.

Note that if you have a 12 check with an 8+ effect, Iron will won't stop the 8+, only the effect labelled with "fail".