I tried something a little different, and was able to get some success.

When I create a volume with the nfs volume type, that is when I get the errors on creating snapshots (nfs is what I currently have set as the default_volume_type)

However, when I create a volume with the iscsi volume type (which is a local lvm storage), If I create an instance from that volume, then the snapshot works without issues.

I had seen this entry in my cinder.conf file:
# Enable support for snapshots on the NFS driver. Platforms using libvirt
# <1.2.7 will encounter issues with this feature. (boolean value)
#nfs_snapshot_support = false
nfs_snapshot_support = true

Which I had set to true several days ago, as that seemed that it might be relevant, but it doesn't seem to let snapshots work when backed by the nfs storage.

Do I have something misconfigured in my nfs configuration in cinder?

Here is what I have configured for both lvm and nfs in my cinder.conf file:
[lvm]
volume_backend_name=lvm
volume_driver=cinder.volume.drivers.lvm.LVMVolumeDriver
target_ip_address=10.61.157.80
target_helper=lioadm
volume_group=cinder-volumes
volumes_dir=/var/lib/cinder/volumes

[nfs]
nfs_shares_config = /etc/cinder/nfs_shares
volume_backend_name=nfs
volume_driver=cinder.volume.drivers.nfs.NfsDriver
nfs_mount_options = rw,_netdev,bg,hard,nointr,tcp,vers=3,noatime,rsize=65536,wsize=65536