Should I review for a new journal whose publisher is unjustifiably listed in Beall's list of predatory publishers?
You need to ask yourself a few key questions:


What is the purpose of your reviewing any article? If it is to be listed in the annual acknowledgement of reviewers for Big, Prestigious Journal X, then don't review this article.  If it is to contribute to the scholarly process (and to pay-it-forward for the next article you submit somewhere) - then proceed.  
What is your impression of the journal/publisher? They can't be entirely/purely dishonest, since they have, in fact, sent the article for peer review. (The truly bad actors don't bother!)


Form your own opinion of their offering, and do consider that it can take longer to review a poor manuscript than a good one.  Then, invest your time in what you value.