Not sure about Roam, I've been using Obsidian, and my purpose is for personal, making note archive offline. So never had any need for collaboration. But with Sync and Publish features, maybe there is a possibility.

Roam seems to be working on it. I’m unsure the status as I haven’t checked in a few months.

I think Roam has been fully collaborative since the launch. The browser keeps the whole database in IndexedDB and syncs it continuously with a WebSocket streaming Datomic-style transactions.

Roam: yes Obsidian: unsure (I think not)