Is it permissible to take a loan from a bank that does not deal in usury, for someone who does not have enough money to get married, knowing that some consider this as cooperation with the bank?

If the bank offers you a benevolent loan (qard hasan) without usurious interest or an impermissible condition, then there is no harm for you in borrowing from it for marriage or other purposes. It does not matter if the bank's funds are mixed. The important thing is to ensure that the loan is free from any impermissible condition.