What you describe doesn't sound accurate concerning the topology.
Router vpns don't point to any "servers" nor are servers involved. What you describe is a site to site vpns which are router to router vpns. This does create a secure transport for server client communications over this vpn network which runs over the internet.
Since you have gone to a cloud solution, which means you have no access to their router/firewall, I see your only option to be putting a client vpn on the server.
This would concern loading the Draytek client vpn software on the server and having the server logon to the main Draytek router. The server would get a ip address from the router in the range of the local subnet [use mac filtering to get it the same one every time]
This does present a problem though concerning your access to the server. Unless the client vpn can do split tunneling, you will lose access to the server. If there was another nic in the server this wouldn't be a problem. If you were virtualizing the server you could have multiple virtual nics so this wouldn't be a problem either.