If I request contact information, but SeekOut can't find it, does it count against my monthly limit?

No.

If you request contact information for someone and we can't find a valid email address or phone number, the number of contact information credits you have remaining will not be decreased.

As an example, assume you have 100 emails remaining in your monthly limit and you request email addresses for 10 new people. If SeekOut returns good email addresses for 8 of those people, but can't find good addresses for 2 of them, you will have 92 email requests remaining.