You can earn/redeem VS miles on CO (not tried) and earn/redeem CO miles on VS (which I have done) but not transfer between them.
You can currently freely exchange miles between UA and CO which allows you to redeem VS miles on UA (indirectly) and vice versa.
You do not need to wait for the merger to do this - you can do it now.
In fact after the full merger next year all this will change as CO OnePass will close and there will be just MileagePlus which has not connection with VS.

For now the CO/VS flights are codeshares but they are not UA codeshares and very unlikely to become so.