If it was relatively recent, I would suggest you do because even if you don't they will find out through the National Consumer Inquiry Council (NCIC) all via computer nowadays then they could cancel you for lying.
If it has been more than three years I wouldn't worry about it because even if they found out it probably wouldn't count against you.
Remember, if you think a conviction has been removed from your record by attending traffic school that isn't neccessarily the case. Actual convictions and numeric demerit points are two ENTIRELY SEPERATE matters.
While your points may be erased, the conviction itself probably still remains and is shown as a paragraph descrbing the details of the accident and why you were at fault and what action was taken which is actually what insurance calculation personell go by when determining your policy premium rates.
In Nevada, you can have up to three numeric demerit points per conviction removed by attending a traffic safety course hoever, if you manage to accumulate 12 points in a twelve (12) month period your license will be suspended for 30 days pending a review hearing.
For a through explination of what I'm describing, go to: http://www.dmvnv.com/dlpoints.htm