I do not believe that you can NFS export a VFAT filesystem.
I beg to disgree. You should be able to export any filesystem mounted by any file-system support module. SImply because in order to mount any filesystem the file-system support module (e.g. vfat.o) must present the system with vnodes (the very thing that NFS exports). If you can mount it (& see it as a llinux (UNIX) file-system - then you can export it via NFS).
Indeed, I recall a very clever friend of mine advising me to export a vfat partition via nfs to work around some permissions(orthelackthereof)-related problem with said vfat partition on a super-short-term basis.