Is the wife obligated to fulfill a vow by giving money to the person mentioned, despite discovering that he is not deserving, or is it permissible to give the equivalent value to someone who is deserving?

Whoever makes a vow is obligated to fulfill it in the manner in which it was vowed. If what your wife conditioned her vow upon—which is getting pregnant—is fulfilled, then she must fulfill it to the person for whom she specified it. A conditional vow is prohibited, but it is obligatory to fulfill it if the condition is met. If the vow was made to Allah and she specified it for a person, then it becomes clear that he is a dissolute person (fasiq), it is permissible to redirect the vow to someone else who adheres to the Sunnah.