Here is what i did to get it working on a Synology DS716+II (8GB) DSM 6.1.1-15101 Update 2, with both Vero 4K and Raspberry Pi 3.
First enable NFS and assign NFS permissions according to this link https://www.synology.com/da-dk/knowledgebase/DSM/tutorial/File_Sharing/How_to_access_files_on_Synology_NAS_within_the_local_network_NFS
After that you have to change permissions for the folder via File Station.
Open File Station, right click on the folder you want to use as NFS share and choose properties.
Select the Permission tab, and click create > and select Everyone from the list in User or Group, and check what what permissions you want, I choose Read and Write.
The second part was not necessary on earlier Versions of the DSM, but it has to be done now, even though it might be a security risk.
Thats all you have to do to get NFS working, I did not edit any files,.
Hope this helps.
/Thomas