Would it be sinful to hide such information from the person seeking it? Would it be sinful to provide the information?
Jazakallah for requesting information from the institute.
Has the person on whom the background check is being done changed his/her lifestyle for the better? Human beings are fallible, sinful and do go astray. However, with Allah Ta’ala’s guidance many do give up their unacceptable lifestyle, make tawbah and try their best to uphold the sunnah and Allah Ta’ala’s commandments. If this is the case with the said person you write about, then it is better to conceal the person’s past.
However, if the person has not changed and still displays unacceptable traits, rather than reveal what the person’s negative behaviour is, suggest to the interested person that he/she should be careful in making their choice and think seriously before making a proposal to this person. Suggest another more acceptable match. May Allah Ta’ala guide all of us towards living our lives according to His commands and may He guide us to give up wrong. Ameen.
And Allah Ta’ala knows best.