I've had a VXFS filesystem get corrupted and now it won't mount.
Can I run a fsck -y on the raw disk device or should something be
done within veritas? Veritas does not see the disk at the moment.

Bummer - I hate when that happens.
It matters what you mean by 'raw disk device' - If this was a vertias filesystem that was mounted as a partition, fsck won't be a problem. If this was a veritas filesystem raw Sybase disk then fsck I believe would fail (since it's not a real filesystem but just a Sybase raw partition controlled by Veritas).
Hopefully you had saved in the past the information needed (I don't recall all of it off the top of my head) -
If the drive failed, then there is a procedure to follow within vxdiskadm of removing and installing - but you should have the old info to know exactly which device you are dealing with.

Is there a log on the file system?

First make sure the disk group is imported with:
vxdg list

If not, import with:
vxdg import disk_group

If that fails, try:
vxdg -Cf import disk_group # assuming this is not a cluster


Then start the volume(s):
vxvol -g disk_group startall

If that fails, try:
vxvol -f -g disk_group startall


fsck the file system:
fsck -F vxfs /dev/vx/rdsk/disk_group/volume

If that fails, try:
fsck -F vxfs -o full /dev/vx/rdsk/disk_group/volume

Mount it up:
mount -F vxfs /dev/vx/rdsk/disk_group/volume /mount/point

Be sure to replace disk_group and volume with your actual info.

Good luck.

If an actual disk failed, and was not fault tolerant, it will be necessary to rebuilt the volume (and maybe the disk group) and restore the data from backup. If it is RAID 0 ir 5 and has a log you should be able to get it back easily.