I say it can. I think comedy and humor are a part of life as much as death and fear, and using humor in a film doesn’t take away from the gravity of its subject matter, but can be used to evoke emotion and power.
That said, I do feel that Jakob the Liar didn’t just use black comedy in its portrayal of the story, but also was somewhat racist in its portrayal of Jews. This I don’t feel is acceptable.
At several points in the movie, stereotypical Jewish music is played while certain characters are sneaking around the ghetto. I feel that this plays right into the cunning and shady image Jews were being portrayed as during the 1930’s and 1940’s and before. When Jakob is away, Frankfurter and company sneak into his house and try to find the purported radio. They tiptoe through the house while the music plays, and it really gave me a feeling of a pack of blundering thieves wandering around the house, not smart enough to pull off a good heist. I don’t know if this is what the director Peter Kassovitz was going for, but this is what I got.
Also, I felt the happy ending was SO contrived and un-fitting. The holocaust is about injustice, terror, death, and despair. That was the reality. There were very few happy endings. I feel like the honor Jakob had in dying with such dignity was lost when somehow the Jewish transport ran into the Russian soldiers who liberated them. Really, the movie had been driving towards the final decision of Jakob: would he reveal his lie or would he not? The lie was what everyone had relied upon throughout the movie. Jakob had given them hope. Would he crush that hope with his revelation, or would he prolong it? It doesn’t matter because of the ending. Kassovitz really pussied out when he ended the movie on such a happy note.