Posting peer reviewed but not yet accepted papers to arXiv
I'm not a lawyer, but their definition of "preprint" says:


  This is the author's own write-up of research results and analysis that has not been peer reviewed, nor had any other value added to it by a publisher (such as formatting, copy-editing, technical enhancements, and the like).


Note all of these - formatting, copy-editing, technical enhancements - are done by the publisher's staff. Peer review is not usually done by the publisher's staff. So I'd say you are clear to post revised-but-not-yet-accepted papers to arXiv.

In any case the worst case scenario is probably them sending you a warning asking you to take down the revision (I consider this rather unlikely too - even if it's against their policies, they would first have to notice, and then have to decide to enforce). So you can probably do it without incurring too much trouble. If you're very worried, you can also ask them.