Acutally, fsck in OS X runs a program called fsck_hfs to repair HFS+ partitions.
The original fsck can't do anything for HFS+ partitions. It is used to repair UFS partitions. Inodes, link counts, data blocks, etc, don't exactly correspond the same way with HFS+.
fsck_hfs uses the same diagnostic and repair libraries as Disk First Aid therefor there is no benefit of running fsck over Disk First Aid.
It has been my experience with UFS that if you have to run fsck, you're pretty much fscked.
Thanks to JFS, fsck is unnecessary.