server is connected to main Switch L3 which is connected to VRRP Cluster with configured gateway on Cluster's Virtual IP.
It is almost exactly as you say, but not Main router but VRRP Cluster should have configured OpenVPN.
In theory and my idea it should work (as you said).
No mater which router is currently in use according to VRRP, user (laptop) will be connecting to currently active router's IP (according to DynDNS). But I currently I have no opportunity to test that solution.
But let's go further. What will happen if VRRP change current active router?
Because session stared on one router won't be transferred to another.