I don't think so. American leftists might suffer from a complete lack of self-respect, but chauvanist Muslims have the exact opposite problem. I don't think they would desecrate their own mosque, and certainly not with symbols that are so anti-Jewish (they would have at least added some stars of david to the field of swastikas, or something). It just doesn't feel like a hoax.
Hoaxes tend to be scatterbrained, sloppy affairs; real hate crimes tend to be on message. Whoever put those swastikas up cared about one thing: swastikas. It seems geniune enough to me.