Ok, that makes sense... it really is a backup strategy question. I went down the cifs route based on some comments from a colleauge who probably misunderstood my question to him (or I misunderstood his answer!).
I'll take a look at VDR and Veeam but I suspect these will not be priced in reasonable proportion to the cost of VS Essentials.
I don't see any reason not to enable ssh on the hosts, but that's just a shell, not a view of the file system. I'm guessing the approach with that would be to script out file copy operations against the host through ssh, copying the the stuff back to the other server where it can be made available to whatever form of backup you've got (tape, more disks, etc).
I'm marking this question as answered because I originally put it in terms of cifs on the host, and it is clear now what the answer to that is. I would like to continue this discussion around the strategy for backing up the filesystem of the host, by which I mean backing up the VMs.
Thank you all for your advice!
Chris