The black cats are all Butch from Tom and Jerry.The cats in "The Cat that Hated People," "Bad Luck Blackie," "Ventriloquist Cat" and "The Cuckoo Clock" are all black just like Butch.
"Sgt. McPoodle" and "Dan Magoo" are just characters that are played by Droopy.It's a possibility.
Spike is the same Spike as the one in Tom and Jerry.After all, they look the same.
The guy who tells the "literal" story in "Symphony in Slang" has a name; it's just not mentioned.The Big Cartoon Database identifies him as "John" so as to match "John and Mary" in some of Tex's other cartoons.
George and Junior did not commit suicide at the end of "Half-Pint Pygmy" and are the hunters in "Lucky Ducky."The hunters bear a strange resemblance to them...
Screwy Squirrel dated a young Slappy Squirrel.Also included on the Animaniacs WMG page. After Screwy's death at the hands of Lonesome Lenny, Slappy became bitter and cynical, never overcoming the grief.
Conker the Squirrel of Conkers Bad Fur Day was the illegitimate lovechild of Screwy and Slappy.Conker is basically a more modern version of Screwy, with the same red fur color.
B.O. Skunk and the female skunk he meets at the end of Little Tinker are Pepe le Pew's parents.Pepe resorts to even more aggressive methods for finding love, perhaps after having been coached by his "father" at an early age. And the French accent is fake (B.O Skunk himself puts on a fake French accent at one point).