How will macOS behave when creating folders in /private/var/folders to mount a NFS share with?
No.
This is a system directory that contains things like logs, databases, your sleep image, etc. It's not a directory that you should be mounting file shares to. The purpose of the /private directory has already be discussed in the following posts:
- What's the "Private" directory in OS X for?
- Snow Leopard *private* folder?
Even the automount service doesn't mount shares to that directory, it's mounted in /Volumes.
Your best bet would be to either mount the share in a shared user space (i.e. /Users/shared) or within the users own home directory.