WLP670 is a blend that I think is very similar to what your asking about. Obviously both yeast get pitched at the same time. I think the sacc gets going fast and the Brett is slower and cleans up all the leftovers. Assuming this is true, I wouldn't think it would matter.
I'm not a big fan of that because I don't like leaving the full load of primary yeast around while the Brett does it's work. I know the Brett is supposed to clean up the autolysis byproducts, but I have had great results racking into the secondary and then pitching the Brett. I just think leaving a primary yeast at warm room temps for a year like the Brett likes is not a good idea.
That is the first time I heard of that issue, indeed, the blended products have both and must be pitched "together". White Labs Berliner Weisse blend is an example, as is Roselaire. Still your point about autolysis is seemingly a good one, at least intuitively. I wonder if the Brett metabolizes the autolysis byproducts? If so, then some yeast leftover would be a good thing.