Yup, but he's actually even more scarier when he's really mad. In my fanfiction, when Sly goes to rescue Penelope while Ludwig is trapped and almost choking between a gear, he sees Sly taking Penelope between his arms and goes crazy: he smashes the gears and starts running to them like an... Animal. On four paws, I mean, and does not even speak, just roars.
They also appear in my Kingdom Hearts/Sly Cooper crossover. In it (KH is a game between Disney and Final Fantasy), Ludwig is an evil character just because Hades promises him to give him Amelia back if he follows his orders. But in the end, the god says: "Go and take her, you just have to found her" and Ludwig jumps in that "soul-pool" (that green thing with the many souls where Hercules goes too to rescue Megara in the Underworld), he is so happy that he does not realize that Hades had fooled him, and Ludwig dies when he finally sees her, and gives her his paw. (Because, if you remember, Hercules got old but didn't die because he was a god himself)
Eheh, she's cute indeed, I think it too. She has a genetic thing that makes her so small.