That depends on how you define utilitarianism though.

That minority also factors into a utilitarian's assessment of what will maximize happiness. If 10% of the population hates the 0.1% minority, but oppressing that minority would also harm them, then you have to factor in the relative harm caused to them as well, not just in raw %'s, but also in terms of if the value given to the 10% from their oppression would outweigh the harm done to those being oppressed.

Furthermore, I'd argue most utilitarians would argue that the very hate towards that minority in the first place is what causes harm, not the minority themselves. The best utilitarian action to take would be to reduce the hate for that minority, and increase their acceptableness, rather than oppress that minority to satisfy the 10%. Especially considering we know this tends to not just be a one-time thing, and that hate will likely continue, leading to further oppression over time, and harm not only to the minority, but also to the mental well-being of the 10%. Thus, the best course of action would be to eliminate the hate, not the minority.

Of course, utilitarians aren't a monolith, but that's at least how I would interpret the situation.