There are certainly a minority of major brands that operate as advertisers with awareness campaigns — sponsored hashtags are a good example — but if you read the Twitter filings, it’s very clear that their focus is performance based advertising — and that’s where they see their future, too.
Maybe a decade ago you could have said that advertisers were just trusting platforms to deliver value, and that ad-fraud could make or break a platform if they got caught, but that’s not true anymore, it’s a much more sophisticated market. Advertisers aren’t (as) dumb (as they once were).
Brand safety is a whole other kettle of fish — that’s a concern across all types of advertising, and not relevant to the audience, rather the content of the platform.