Yes, you still need Web SDK with Event Forwarding.
Here's how the data flows:
your website --> Web SDK --> Datastream --> Event Forwarding
If you were to also use Web SDK to track your Analytics data, then the data would flow like this:
your website --> Web SDK --> Datastream --> Event Forwarding
--> Analytics
i.e. you still have 1 Datastream, but you configure 2 endpoints in it (Event Forwarding and Analytics). Take note, though, that the same data that is tracked through Web SDK will be consumed by both Event Forwarding and Analytics.