Because ROOM was designed with the purpose of breaking out of the old "boxed-in meeting" paradigm, we strongly suggest that you use one to get the most out of the ROOM 3D experience.
So, although it is possible to take part in a ROOM meeting without a webcam, you won't be able to enjoy the immersive 3D experience and all its amenities.
To learn more, please refer to these articles:
What are the technical requirements to use ROOM?