The Fresh Prince Project - S1-E1
Revealing mistake: When Will screams in front of the mirror, imagining himself turned into Carlton, something went wrong making the composite shot and not only you can actually see the line of separation between the two frames, but the superimposed one exposes a bit of the mirror woodframe before it wiggles into the correct position and covers it up. (00:11:30)
The Fresh Prince Project - S1-E1
Revealing mistake: When Will staples his Malcom X poster to the wall, the wall bends back and forth for a second or two.
Revealing mistake: When Phil is looking for Will who is in Ashley's room he slams one door shut and the set wall can be seen to wobble. (00:11:00)
Clubba Hubba - S1-E3
Revealing mistake: During his first conversation with Dr. No, Will Smith mouths "strings of Arabians" as Richard Roundtree says it (it can't be a line he rehearsed with Carlton, because his character has no clue about that branch of conversation). (00:11:00)
Answer: No, it's not Whoopi Goldberg herself, just like that's not Prince or Ray Charles. The limo is filled with celebrity impersonators, but they're all uncredited and I could find out who played them.
Bishop73