The problems with using "et al." have been discussed at length on this blog post [1] and probably elsewhere on mathoverflow. However, these authors have left you in a slightly ridiculous situation if you try to give a full citation in the body of your text. So it seems that biting your tongue and using "et al." is the best way forward in that (apparently very unusual) situation.

It seems particularly bad to me to not list all the authors of a paper in the actual bibliography entry for the paper. Personally, I would list all of them in my submitted version and see whether the journal editor wants to force the matter.

1: http://sbseminar.wordpress.com/2010/02/21/et-al-is-unethical/