All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
There is no doubt that dealing with usury and/or interest is a major great sin. It is more appropriate to prevent whoever deals with usury and/or interest from leading Taraweeh prayers or obligatory prayers or any other prayer. Nevertheless, if he leads the prayer, praying behind him is accepted. 'Abdullaah Ibn 'Umar used to pray behind Al-Hajjaaj Ibn Yoosuf Ath-Thaqafi despite the latter being a dissolute, oppressive and unjust person. However, as previously indicated, the brothers running the mosque should choose a pious Imaam to lead the prayer, especially since the opinion of some scholars is that the prayer behind a dissolute person is not valid, but the majority of the scholars consider that praying behind him is accepted.
Allaah knows best.