None of us are involved in the hiring process, so we may not have the information you are looking for.
From the CBP FAQ sheet:
Pre-employment Requirements consist of a thorough background investigation, medical examination, fitness test, and drug test. If your background includes past or present arrests, convictions, dismissals from previous jobs, debts and financial issues, excessive use of alcohol, use of illegal drugs, and/or the sale and distribution of illegal drugs, you most probably will be rated unsuitable for this position. You may also be subject to a polygraph examination.
Law enforcement positions have been able to use poly as part of the hiring process for years. Not all agencies require it unless there is a specific reason, such as part of an investigation. My take on this is that you might have to take a poly, not that you will. The CBP is simply being proactive and ensuring you are aware of the possibility.
You're allowed to have a life, you know. I read it in a manual somewhere. - Eugene Matuzak - Timecop