Am I sinful for helping my friend work in a hotel that serves alcohol, knowing that my intention was to keep him away from the lands of immorality? Is my friend's money unlawful due to his work, and is it permissible for me to accept his gifts, borrow from him, or enter into a financial partnership with him?

You have done well in helping your friend move to a Muslim country. His work in a restaurant that sells alcohol is permissible as long as he does not sell the alcohol himself or assist in its sale. The prevailing opinion is that the mixing of money does not prohibit dealing with it unless it is known that his salary comes from unlawful earnings. The Prophet, peace and blessings be upon him, and his Companions dealt with the Jews despite their involvement in usury and consumption of ill-gotten gains. It is permissible to borrow from your friend's money or accept his gift for your children, because the Prophet, peace and blessings be upon him, dealt with the Jews and ate from their food.