Does utilitarianism agree that it might be true that society as a whole would benefit by having some group discriminated against?

No. Utilitarianism basically works on the principle of making the largest number of people possible as happy as possible. While the ability to discriminate would make one subset of a population happy, it would result in the unhappiness of a larger subset of that population, making a net unhappiness. It is therefore against the idea of utilitarianism to discriminate.

However, if more than one group could be discriminated against, and if all groups have equal ability to discriminate, it may be the case that in certain situations and with certain permitted levels of discrimination that it indeed results on a net overall happier population. In this scenario, discrimination would acceptable to a specific degree.