Tuff Puppy/WMG

Keswick is a Digimon
Perhaps Gizamon, or something new.

Kitty is half-human
She's the most human-like character on the show, and Dudley is half goat.

Brian from Family Guy is Dudley's father.
There's a strong resemblance, and Brain has been known to have fathered illegitimate children. I'm not the only one who's noticed.

Butch Hartman is a Harry Potter fan.
The main character's name is Dudley. Peg also seems to have a personality similar to Molly Weasley. Also, Kitty has very prominent green almond-shaped eyes like Lily, Harry and Albus Potter have. Also, there are several episodes that focus on invisibility, time-travel and mind-reading. Several minor characters are also similar in character to Luna Lovegood. Zippy also appears to act a bit like Bellatrix at times and Dudley and Kitty's relationship is much like that of Ron and Hermione. There are also hints of this in his other works.

Kitty is part Leafeon.
In the first episode, Keswick said that Dudley has “a dash of billy-goat”, so it may be possible. Also, Kitty dose look quite a bit like a Leafeon with a similar build and color-scheme as the grass-type eeveelution.

Kitty:

Leafeon:

Dudley and Kitty will eventually be paired up.
Of this I am certain, especially due to the possible opposites attract factor.
 * Turns out to be true thanks to Word of God.
 * Where did Butch say that?

Dudley being part billy-goat will a Chekhov's Gun
I have a feeling that will become important later.

Kitty is a former O.W.C.A. agent
Because Shut up.
 * Alternately, T.U.F.F is a splinter group of O.W.C.A.

"The Third Dimension" from 'Toast of T.U.F.F' is The Ghost Zone

 * Just look at it.