Vector clocks? Sure. UTC clocks? Not a chance in hell I'd ever trust them for a reconciliation protocol. I've spent way too much time around the internals of hypervisors, and seeing how various OSes (and versions of them) do and don't keep time well in virtualized environments gives me zero confidence. The fact that any two given cloud VMs agree on the time within 500ms is a testament to the sheer bullheaded determination of their administrators.
Simply, you cannot trust timestamps between two machines to determine ordering. If you do, you will have a bad time sooner or later (so to speak).
AFAIK only spanner uses real time as a core primitive. They don't use ntp ;-)
Monotonic sequence numbers loosely based on real time are common, since you can correlate the sequence number back to an actual time to look at logs, etc. Time skew wouldn't break the protocol, just make it annoying to correlate after the fact.
And of course any leasing system uses bounded clock skew rate between hosts, but NOT bounded absolute skew.
