It's years after your post, but I still feel compelled to respond to it, billyed.
No, Davis did not "gain weight on purpose" for this role. She was naturally heavier at that particular time in her life and her matronly figure was the result of the weight gain that often comes with middle age -- Davis was 47 when she made this film -- as well as the onset of menopause. Many women gain weight during menopause, and Davis was no exception. Also, De Niro didn't gain weight because "LaMotta got fat when he got older." De Niro bulked up because that's how Jake LaMotta looked during his fighting years, not when he got older. LaMotta not only raged like a bull, but was built like one too. Don't confuse bulking up with fatness. Watch the film again and you'll see the difference.
I'm not sure how you define "a fuss being made," but yes, a fuss was made when De Niro gained weight for his role in Raging Bull because up to that time actors weren't willing to gain a significant amount of weight for a role regardless of the reasons or price. De Niro did so because he's a quintessential Method actor and as such wanted to not only act the part, but look it as well. It was a first for an actor to naturally increase his weight as much as he did without the aid of a fat suit and yes, it did cause quite a bit of discussion at the time, what you might call "a fuss."
Sorry cookie, while it was unusual at the time De Niro gained weight for RAGING BULL, Shelley Winters beat him to it for THE POSEIDON ADVENTURE seven years earlier. It was in her contract that the producers had to pay for her weight loss at a fat farm when filming ended. By coincidence, Winters & De Niro were good friends having made BLOODY MAMA together for Roger Corman years earlier.