I have Dish, sound bar and Roku Ultra.
HDMI from Dish to Sound bar input connector
Sound bar HDMI output to TV HDMI input
Normally I think you go from Roku HDMI output to TV, but that would ignore the sound bar.
Can I go from the Roku USB to my sound bar USB?
No, you can only use hdmi for video and audio. The usb on the ultra is for reading files like pictures or music.
Assuming your soundbar's HDMI/ARC port is connected to the TV's HDMI/ARC port, then you should be able to connect your Roku (and your Dish or anything else for that matter) to another HDMI port on the TV and the sound will route to the soundbar (assuming the TV is in ARC mode).