Tex Avery MGM Cartoons/WMG

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...