What happens when you put an invalid mount in fstab?
 

I'm not sure if a shared nfs mount will be seen on the particular box since it's in a DMZ.

So if I for the new entry and it doesn't see it, what, if anything, will happen?

I once made an error editing fstab and the result was that my machine would not boot. I had to go in by recovery mode from Grub and fix the error (using nano).

Agree - in some OS's you can get around this and boot but obviously the invalid mount will not be available.

I would expect that you would get an error that it can't be found or doesn't exist at worst. If you have an incorrect entry for / that's a different problem. Don''t know about the DMZ part.

flshope was correct. wouldnt boot after issuing reboot command. editing the file is recovery mode restored it.

If you include the "nofail" option in that fstab line, then the boot sequence will continue whether or not that mount succeeds, assuming that the contents of that mounted filesystem are not essential for booting, of course.