Can Hitler ever be funny?
Mel Brooks, Gene Wilder and Zero Mostel somehow managed to pull it off in The Producers, but it's really, really hard to make a Hilter-themed performance that's genuinely humorous rather than abhorent and disgusting.
Rosanne Barr's biggest problem in this effort is that her talent and comedic gifts aren't even a small fraction of the great artists mentioned above...as a consequence she merely comes off as repulsive and annoying.