emont
Kroll doesn't have an application--they just ask for your name and SSN then they get the rest with their own research. If there's a huge discrepancy or they have trouble getting ahold of one of your employers they'll contact you. Just make sure whatever you put on your application is as close to accurate as possible.
emont is pretty much right on the money and I had similar experience with kroll. Some people have different experience because:
1. Different schools ask kroll for different areas to check
2. Each employer has different policies regarding background checks. Some are absolutely set on limiting access to employee info, other than basic stuff like length of your employment, etc. (mostly due to HR policy and legal issues)