Are you connecting the RICOH THETA camera to your computer with a USB cable? This is the recommended method. However, I wanted to confirm what the connection is between computer and and camera.
Are you planning to do the object detection on Linux?
If you stream using a USB cable at 4K 30fps, you will need either a V or a Z1. The V is cheaper. If you have the budget, the Z1 has advantages in 24x7 streaming. However, it is more expensive.
The streaming output is equirectangular. The video stream is stitched inside the camera.
You can only get a RAW image with the Z1. It will not be a video stream.
I do not know what image_raw does on ROS. However, if you are trying to get a normal web cam video stream, you can get the video stream on /dev/video0 with v4l2loopback.
This topic may be of interest to you.