How unhealthy is shisha smoking?
Since shisha is tobacco, smoking it likely involves some of the same ill effects as other types of smoking. However, whereas cigarette smoke fills my chest with a harsh, burning sensation, I can barely feel shisha smoke in my lungs. Because of this smoothness and the fact that it is light, filtered, and cooled, I would say that it is very probably the safest form of smoking there is*. And because it takes a few minutes to set up and then a long time to savor (similar to pipes and cigars), shisha smoking is unlikely to entail that psychological addiction for a quick puff that cigarettes can.
Can I smoke "other things" out of my hookah?
Hookahs have for centuries been a tobacco-related product and the image of them as a pot or opium-smoking instrument is largely of Western origin. Indeed, it is considered very poor ettiquette in some circles to smoke anything other than shisha in your hookah! However, should you choose to place something else in your hookah bowl, even regular shag tobacco, it is generally a good idea to mix your substance with regular shisha, molasses, or honey so that it is not too dry. If what you are smoking is too dry, it is likely to burn away too quickly, denying you the relaxed puffing inherent to a good hookah experience.