Thanks all.
The conclusion there seemed to be that it ought to work just fine, but should be tested. Well, I'll test it and see if anything interesting comes up. If anything LVM snapshots will be less tricky than NetApp snapshots as LVM has access to the OS's local cache buffers, whereas the NetApp doesn't (though presumably the OS shouldn't/doesn't do any write caching when writing to a network FS).
Try - [GENERAL] A few questions to real pgsql gurus
Ben