I create monthly videos for our CEO to communicate with our employees. I would like to use some music from this site for the entry and exit graphics; however, there are never any credits on these videos, so do I still need to include attribution?
You should, yes. There are alternatives to end credits, for example, you could have a little text popup, music video style, at the moment the sound is playing. Or, if even that is too much, you can ask the sound uploaders via private message for permission to use the sounds without attribution.
If you contact the Freesounder who contributed the music you could ask them to waive the attribution and no advertising* conditions on the Freesound licence. They may want renumeration, (I would).
* music to accompany a corporate logo sounds like advertising/promotion to me .
You may not use this work to advertise for or promote anything but the work you create from it.http://creativecommons.org/licenses/sampling+/1.0/