Yes, Napoleon needed Squealer as a propaganda mouthpiece to convince the other animals to keep him in charge and support his ideas. By all accounts, Napoleon was not a successful talker.
Snowball was a more vivacious pig than Napoleon, quicker in speech and more inventive, but was not considered to have the same depth of character. All the other male pigs on the farm were porkers. (chapter 2)
Napoleon is ruthless and power-hungry. He uses other pigs like Squealer to talk for him. He uses the dogs to control people. Therefore he does need Squealer and Snowball. He uses Snowball’s ideas, and Squealer’s eloquence, to convince the other animals to do what he wants. By contrast, Squelaer is described this way:
He was a brilliant talker, and when he was arguing some difficult point he had a way of skipping from side to side and whisking his tail which was somehow very persuasive. The others said of Squealer that he could turn black into white. (ch 2)
Squealer is already more energetic and convincing before the animals take over the farm. He clearly is already an expert at propaganda. Napoleon knew exactly what he was doing.
For more, see:
Read the full text here: http://www.george-orwell.org/Animal_Farm/0.html
Orwell, George. Animal Farm;. New York: Harcourt, Brace, 1954. Print.
"Animal Farm." George Orwell. Web. 05 May 2012. <http://www.george-orwell.org/Animal_Farm/0.html>.