If memory serves me well, yes
A version of Darker Night compatible with DynEnv is included in the same package, as optional mod. If you want to patch DynEnv with the skycolor fix (for bluer skyies) you cannot use the regular darker nights submod though. You should use instead the darker nights version of the hotfix, prepared by Captain America.
Captain America is working as well on a murky waters version of the hotfix, that will restore the greenish waters in some areas (Baltic, English coasts, etc), also originally featured in DynEnv.
Both the normal version and the darker nights version of the hotfix are available on this thread (though NOT in the first page). Ask here for the links if you don't manage to find them.
The Murky waters version is almost completed, and will be soon available for download on this thread.
I think so, but honestly I am not sure about it

as I don't use external cam that much, and water transparency settings were part of stoianm's tasks. Try waiting for replies by him or by other users