Bob Ewell’s full name, Robert E. Lee Ewell, is symbolic because Ewell is a racist like his namesake.
Robert E. Lee was a Civil War general on the Confederate side. Since the Confederates mostly represented southern slave states, the name is symbolic of the racism that Bob Ewell embodies.
The Civil War is very important to Maycomb culture. Most people can trace their families back to it, including the Finches.
Cousin Ike Finch was Maycomb County's sole surviving Confederate veteran. He wore a General Hood type beard of which he was inordinately vain. (ch 9)
In fact, the Civil War is so important to the South that many are still fighting it, in their own way.
The tribe of which Burris Ewell and his brethren consisted had lived on the same plot of earth behind the Maycomb dump, and had thrived on county welfare money for three generations. (ch 13)
Ewell is not a veteran of the Civil War, but clearly his family considers Lee important enough to name him after him.
In Harper Lee's classic To Kill a Mockingbird, Bob Ewell is the personification of poor white trash. He is too ignorant and too lazy to hold down a respectable job, and he spews racist invective with the ease of a seasoned veteran of the Ku Klux Klan. When he is called to testify in the rape trial of Tom Robinson, he proudly proclaims his moral connection to the American South and the Confederacy that went to war rather than succumb to abolition. When instructed to identify himself for the benefit of the jury, Ewell responds as described in the following passage by Lee's youthful, innocent narrator, Scout:
"All the spectators were as relaxed as Judge Taylor, except Jem. His mouth was twisted into a purposeful half-grin, and his eyes happy about, and he said something about corroborating evidence, which made me sure he was showing off. '…Robert E. Lee Ewell!'"
By naming her primary antagonist after the most prominent general of the Confederate Army, Lee is drawing that connection between the fight to preserve the institution of slavery and the racial attitudes that continued to survive well-into the 20th century.