I can only comment based what I've seen/heard in my flying. The only external camera's I've seen used are on SAS. Cameras were generally on forward facing during takeoff and landing.
As for Untied's channel 9. I'm not sure what people are assuming it is or isn't, but if I recall correctly, its just whatever ATC the pilots are communicating with, and their responses. On occasion you'll hear other pilots reading back instructions, that's about it. Any other communication .. such as those within the cockpit, or if a pilot were to contact the company are not included.
Most of the time UA pilots will make it available. Some will turn it off for takeoff and landing. Frankly, its not very entertaining most of the time...particularly over the Pacific at 4am local time.