Update:
I was able to make the client use the IpNetDriver, but it leads to an error saying that the unique_net_id is incompatible. I tried following the advice from this post (UE4 incompatible_unique_net_id) but it just leads to the server crashing once the players connect.
Could it be that Unreal is designed to not support having the client and dedicated server not use the same online subsystem?