I daresay.
However, from what I have seen (and tasted) thus far, if the Ethiopian truly comprises only a third of that blend (Brazilian tends to be very robust) it will be pretty much overwhelmed, smothered and stifled.
My sense - and I have been experimenting with blends over the past year, and belatedly, and reluctantly, came to the realisation that the more 'standard' proportions don't always quite work if you want the qualities of the lighter, less roasted - coffees to come through.
These days, not least because I love Ethiopian - because 1) it is lightly roasted, but 2) because I love its clean, clear, "bright" qualities - I know (from experience) that it will be smothered if strictly proportional quantities are used with other coffees, i.e. if one uses a third of each.
In my experience, if you want the qualities of the weaker coffee to com through, you need to adjust the percentages, or proportions; for two blends, 60/40 or 70/30 - in favour of the Ethiopian would work if you wish the features of the Ethiopian to come through, rather than merely temper the excesses of the others.
For a blend of three coffees, unless I am using three different varieties of Ethiopian coffee (which I have done, and where I will strictly adhere to the thirds rule), if, for example, I am using Brazilian and Colombian, I would use 40% Ethiopian and 30% of each of the other two, or - even, at a pinch, 50% Ethiopian and 25% each of the others, or 50% Ethiopian, and - depending on strength (and roasting) 30% and 20% respectively, of the others.