As you can see in the screenshot, The thighs of this woman have no poke through in the iClone 8 viewfinder. There is indeed poke through, but I have the opacity on her legs set to zero. Yes, I do see the problem in her shoulders too.
Let me head you off at the pass now: Conform doesn't help. Loose fitting and increased size doesn't help, and her bodysuit starts to bunch up when I try it. Yes, I also see her toenails poking through
The thing is, I can get around this for extreme poses with selective key framed opacity. It works fine for a native render, but nothing makes any part of her skin go  invisible in IRAY

On the left, we have a boring native render. On the right, we have Iray with her totally clear skin clearly showing through her bodysuit.

I've made the entire opacity map black. I've even deleted the diffuses texture. That just leaves a gray poke through.

On the Iray materials side, I've selected her legs and reduced the opacity. Nothing. The only thing I can think of is maybe a clear iray shader (if that exists.).

 Besides changing her outfit, is there any way to get Iray to respect opacity when conform fails?

20% of original size (was 2560x1440) - Click to enlarge

I ran into this problem as well. I'm guessing it is some sort of bug. The work-around I found was to turn off Subsurface Scattering for body part (in the materials tap of the Iray plugin). For the images below, the opacity map for the legs is full black.

Before:
20% of original size (was 2560x1440) - Click to enlarge

After:
20% of original size (was 2560x1440) - Click to enlarge

Thank you!

I'll give this a try. There had been a serious drought to any sort of replies lately, and I had stopped looking.

i got the same problem, sss doesn't help what to do?

20% of original size (was 2560x1440) - Click to enlarge

The SSS worked for me. Everything besides human flesh doesn't require any extra tweaking for me so far.
I'd like a shot at making that background transparent.

Yes.
It was my mistake.
I’ve got 2 objects overlapping.
It works great to add a label in normal render but makes a hole in Iray.