That’s true, for OTRv3 users need to exchange messages to start a chat. That is why I talk about “pending” OTR chats above. The chat has to be accepted by the other side before you can send messages into it.
But there is no need for presence status (“online status indicator”) for OTR to work. It even works over IRC. You can try to open an OTR chat and keep using normal chat until your contact is online and accepts OTR chat. The only interactive part is the key exchange, after which devices can send messages while the other device is offline.
As a side note, OTRv4 has an option to start chat with offline contact in the current version of specification:
It depends on sharing prekeys via some (not necessarily trusted) channel, though, so it is hardly an option for DC.