Is it ok to always have the lens hood mounted on a lens, even when carrying a camera in a bag or is it in any way dangerous? Can I have the lens hood mounted all the time or should I put it on only when taking pictures?
If the bag is subject to enough force to damage the hood, then I'd be worried for the lens/camera. There should be no problem leaving the hood on, however it can take up a lot more space. For this reason most hoods can be reversed for storage.
If they can't be reversed, I often take the hood off and place it loose around the lens for extra protection.