He drives a taxi and takes passengers to bars and night clubs

Praise be to Allah.

It is haraam to go to bars where alcohol is sold, and night clubs which involve immoral and sinful things. It is not permissible to help anyone with regard to that, or to take him in his car for free or for payment, because that is helping in sin. Allaah says (interpretation of the meaning): 

“Help you one another in Al‑Birr and At‑Taqwa (virtue, righteousness and piety); but do not help one another in sin and transgression. And fear Allaah. Verily, Allaah is Severe in punishment”

[al-Maa’idah 5:2]

Based on that, if your husband knows that the passenger wants to go to a haraam place, it is not permissible for him to take him. 

Similarly, he should not wait for the people who are coming out of those haraam places, because that is facilitating their coming and going. But if one of them stops him and asks him to take him home or to some permissible place, he may take him there, because that does not involve what we have mentioned above about helping in sin. 

See also the answer to question no. 75443 and 10398 

And Allaah knows best.