[the HP-UX manual says] NFS NFS does not support ACLs on remote files.
Yeah, Solaris says the same.
They do? That's a documentation error, given that they cooked up a protocol to support ACLs over the wire.
Also there is very little info on this NFS_ACL protocol in Solaris docs.
Probably because it's not implemented by a separate server that has to be separately controlled - NFS and NFS_ACL requests both go to port 2049 and are processed by the NFS server.