In American English, none of those words are regularly pluralized in -x, not even tableaus. (Nor bureaus, nor chateaus.) Of course, I'd also say that none of those words are "regularly" pluralized to begin with. One doesn't often need to refer to multiple tableaus or bureaus in print.
In other -x neux, American crossworders may be familiar with EAUX ("Vichy waters?"), but that's definitely a French word, not an English one. Flambeaux is borderline. Beaux appears as an adjective in Beaux-Arts, but that's a borrowed French phrase.
Basically, the "Frenchier" the word, the more likely I'd be to consider it pluralized in -x. For example, I would consider ski chateaux to be humorously pretentious*, but chapeaus to be a solecism. (If you're going to go that far out of your way to use a French word in place of hats, you should spell the French word correctly.)
* FWIW, Google disagrees with my personal intuition about "ski chateaus"; neither phrase is common, but "ski chateaux" is more prevalent in that tiny sample.
In all of these cases, I would expect an American-English speaker to pronounce the final -x as /-z/, regardless of its French pronunciation. See also this Wikipedia talk page.