Its my impression and understanding that the brett to Sacch ratio is of little concern with the 9097 Old Ale blend. The Sacch component of the mixed ferment is so fast compared to brett leading to the slow secondary fermentation by brett. I'm sure you know this but I'm just restating.
If anything the washed yeast, depending on when you removed it from the fermentor, will have a decent population of brett if not more brett that the original ratio at pitch. If you have access to a microscope you can often times tell because brett is much smaller. The packaged yeast is not just a mixed fermentation by wyeast it is probably just a yeast cocktail from two separate pure culture fermentations. Then they checked cell counts via a hemocytometer and mixed each package of yeast according to the desired Brett : Sacch ratio.
So my bet it that if you want to use it in a stout you'd be fine just growing it up in a starter and pitching. The brett will always be out numbered by the extremely fast growth rate of sacch in the beginning of fermentation. However, if you want a funkier presence in your stout pitching the extra vial or a grown up starter of brett will certainly get you there.