It makes sense; English speakers would understand it easily. We might more commonly hear on the news "The proposal was adopted by a margin of 70 votes to 25." Though I suspect that's sloppy usage, since the margin would be 45 Nevertheless one hears that quite a lot.
Hey, Lewis. I would say that this is not the most idiomatic thing I've ever heard. If I may borrow savannah's perfect word: it's a bit sloppy. I think it might be more common to hear savannah's suggestion or perhaps more correctly:
The proposal was adopted by a vote of 70 [yays] to 25 [nays].