I'm guessing you made the scene in poser with limits off, hence when you turn constraints on in carrara your poses snap back to their closest constraints.

In the carrara import dialogue, uncheck the box that says "import deformers." That should fix the problem, at least it does for me.

The mil4 figures have a bunch of poser magnets attached to help with bending, but aren't needed in carrara. As far as I've seen those helper magnets are totally extraneous in carrara and as can be seen in the case of the shoulders there they can actually screw things up. As an added bonus the instances tab in your properties tray will be much cleaner.

I do this all the time and haven't had a problem yet. The figures still bend as they do in poser.

A little side note: Doing this will also kill any other magnets or poser deformers you may have added. In that case convert the deformers you added to morph targets before importing.