Ulla is the true Big Bad.
Along with the "Ulla is a Nazi sympathizer" WMG below, Ulla gradually becomes more and more sketchy as the movie goes on. She even flat out tells Leo that he can either own up to his crimes (making it sound like a bad thing) or flee to Rio with her and use him for every cent (making it sound like a good thing). Ulla is a Nazi sympathizer.
When Max and Leo first meet with Liebkind, he rhapsodizes about Hitler's ability to give an entire apartment two coats of paint over the course of a single afternoon. After Ulla is hired, she takes a day or less to cover every square inch of surface in the office with a coat of white paint. Coincidence? I think not! Clearly, Ulla is a great admirer of Hitler and acquired her speed-redecorating skill in homage to him. This would also explain why she wanted to be involved with the "Springtime for Hitler" production, so much so that she didn't even wait for a casting call before contacting Max and Leo. Counter WMG: It's another joke on Hitler's heritage.
There's already a joke that Hitler came from a "long line of English queens"- the same that Roger is apparently- so Ulla's fantastic super painting speed could be a joke that Hitler had Swedish heritage as well. Not very "pure German" of him. Or that Ulla is a relative.
Leo Bloom is Willy Wonka
In the original 1968's version, Leo Bloom was so traumatized by the whole series of events that he eventually snapped in prison, becoming obsessed with plays and music makers and thinking he's some sort of magical candy-maker. He assumes this "role" upon release and founds the Willy Wonka Chocolate Factory, running the entire thing just like he did with the plays, making this film a prequel to Willy Wonka & the Chocolate Factory. Max Bialystock is Force-Sensitive.
His ability to talk people into things they'd never ordinarily do? That's not schmoozing, it's the Jedi Mind Trick. And in the musical, when he has his meltdown in the middle of "Betrayed" about someone else (Alvin's) life flashing before his eyes, he was really having a Force Vision. Ulla is way smarter than she lets on.
Either she's purposely Obfuscating Stupidity, or she's a Ditzy Genius. Evidence:- She wrote "When You Got It, Flaunt It" completely on her own in less than a day. That takes talent.
- She's evidently in a position where she's introduced riding in a Rolls Royce limo — there's no mention of a husband, so she's not a Trophy Wife. Family money, or money left over from a previous job? She agrees to work as a secretary while waiting for the show to start production because it's not like she has anything else to do.
- Most of her ditzy moments seem to come from the language barrier, and just being a bit of a space cadet, rather than actual stupidity. Or, if you believe this WMG, simply her being a Troll. (I like to imagine she recognized Max and Leo's office as the place where a "crazy person" (ie, Max) yelled at her out the window, and her bringing it up during her audition is her teasing Max about it without outright saying she knows it was him.)
- She encourages Leo to get the hell out of Dodge when Max is arrested. Sketchy, sure, but pragmatic. (And she does apparently support Leo's choice to turn himself in later on.)
Roger de Bris always read Springtime for Hitler as a satire.
Continuing with the Alternative Character Interpretation that Roger isn't that bad of a director as everyone claims he is, what proves he always saw the musical as being a comedy is when he shows up on stage as Hitler and seems positively thrilled when the audience is laughing at his antics.