Brett does seem to require more stain than most of the Sacc strains. White Labs (and the Yeast book that got their information from Chris White) suggest a 0.01% MB. This works well for about half of the Sacc strains that I have worked with. For Brett is seems like 0.06% or 0.1% works much better. I haven't checked MB staining of Brett against a plate or slide culture, but the numbers that I get with the 0.06% MB seem much more reasonable. It also seems to "light up" the cells much better. Also a 0.1M solution of Glycine works fairly well for un-flocculating the cells. The acetic acid MB solutions do a much better job of un-flocculating, however it also seems to strip some of the MB stain out of the cells making the count more difficult and therefor error prone.
Here is some work BKYeast did on this subject:http://bkyeast.wordpress.com/2013/01/26/dyeing-yeast-cells-life-vs-death/
And here is my procedure:http://woodlandbrew.blogspot.com/2012/11/counting-yeast-cells-to-asses-viability.html