I was an avid Animaniacs fan as a kid, then later became an obsessive Marx Brothers fan, so I have seen alot of similarities between the two. Even though, Tom Ruegger (creater of Animaniacs) said he based the Warners on his two sons and one daughter, it doesn't seem to be possible since there are too many things comparable to the Marxs.

1. Each of the Warner brothers' names end with 'O', and describe their personalities (like the Marxs names do). Since alot of vaudeville acts and comic strips had O's in the 1930s, you might dismiss this as proof.
2. Yakko takes Groucho's speedy one-liners and book-learned knowledge.
3. Wakko takes Harpo's madcap personality and boyish charm.
4. Dot takes Chico's will to charm the opposite gender.
5. Hello Nurse is like all the blondes that Harpo chases in films, and is used the same way in Animaniacs by Yakko and Wakko, they often jump into her arms or lap. -- Harpo and Chico did that in "A Day At The Races" to Esther Muir.
6. Wakko's long turtleneck sweater and backwards cap are taken from a scene in "A Day At The Races".
7. The Warners lived in a watertower and were only let out when the company needed them for something, and often escaped the tower when they are bored. --Harpo mentions in his autobio that while filming "The Cocoanuts", Chico kept escaping to poker games and races, which led Harpo, Groucho and Zeppo to run around town looking for him, and when Chico wandered back to the set, his brothers were still out looking for him. It slowed the production of the film since the Marx were hardly ever on set, so the company decided to lock them in their own jail cells on the set until they were needed for filming (Chico's jail cell had its own pay-phone so he could place racing bets from there).
8. Wakko plays the piano. --Harpo played the piano in "Animal Crackers" and "The Big Store"
9. The Warners made fun of current films, like Jurrasic Park, Casablanca, etc. One episode had Yakko playing a private eye and a Hello Nurse comes in, which resembles Groucho and Monroe's scene in "Love Happy".-- The marx films made fun of current film types like gangster films, westerns, and war movies. Plus Groucho would take a character name or situation from a current popular film and poke fun at it when it reminds him of the situation he is in.
10. Many of the episodes had musical segments. Ones that come to mind are Rita singing to Runt while locked up in the pound, and entire music video of Slappy Squirrel rampaging the streets in a red sports car for the song "Little Old Lady From Pasadena". --Many Marx films were forced to have musical segments, we all remember "Blue Venetian Water", "O Solo Mio"
11. Wakko had a "gag-bag" kept under his hat. It was similar to the pockets of Harpo's raincoat, storing all sorts of crazy things, from monsters to food.
12. Minerva Mink was alot like Marilyn Monroe's short appearance in "Love Happy".
13. During the explaination of the Warners history, it is said they performed in many old cartoons which were played in black & white and that the cartoons were so crazy that nobody could make any sense out of them. --The Marx Brothers films were described as being the same way.
14. Wakko mocks Harpo's famous "Gookie" facial expression frequently in cartoons. (A "Gookie" is when Harpo crosses his eyes, puffs out his cheeks, his mouth is open in an 'O' shape, and he tucks his tongue over his teeth. He managed to throw a "Gookie" in every Marx film.) Wakko even sang a hippie song called "Make A Gookie". The only difference between the two, is that Wakko's eyes become swirls because it's impossible to look cross-eyed if you don't have pupils.

If you can think of any that I have missed, please email me and it will be posted.

I must be going