For the first question...the short answer is no. The long answer is no, with an explanation. The dragons don't worship Tiamat. She isn't a god to them, more like a mother to the race. Most dragons believe she is waiting for them in the afterlife. Some dragons don't care, but most do. These dragons believe that Tiamat observes and judges their actions, and that they should seek to make her proud. I guess it might be possible that there are dragons who get angry at non-believer dragons, but it's difficult to imagine they would do anything about it. Dragons don't really care what other dragons do, so long as it doesn't effect them. The skepticism of another dragon has no effect, positive or negative, on another so they aren't likely to care...unless the other dragon is being a dick about it. Then they might get violent.
As for the second question, yes there are laws. The dragons follow a code of conduct and honor called the Lex Draconic. Literally, the Law of Dragons. Most of these laws were set forth by Tiamat herself, but along the way other rules have been added. Most dragon laws concern interactions between dragons, but there are also laws concerning how they are to interact with other races, including humans. Dragons are not forbidden from killing humans, but they are forbidden from taking a position of authority over them. Dragons once did that very thing, and it didn't end well for the humans beneath them.
Similarly, the rules for how dragons resolve challenges is detailed. For example, it is considered an act of dishonor to attack another dragon that cannot possibly defeat you. This law is intended to protect very young dragons, who are hopelessly outmatched against older, bigger dragons. It goes without saying that damaging an unhatched dragon's egg is the worst crime any dragon can commit. Dragons reproduce so infrequently, with only three or four dragons born in a century. If unchecked, killing hatchlings or destroying unhatched eggs could easily lead to the extinction of the race.
Dragons have a number of ways to deal with lawbreakers. The most obvious punishment is death, but it is very rare that a dragon ever does something heinous enough to warrant such a penalty--or, that he gets caught. Examples of crimes that would warrant death include destroying an egg, killing a hatchling, or murdering another dragon in anything other than an honest challenge (i.e. one where they at least stand a chance of survival).
More commonly, dragons are given punitive penalties. This may not sound like much, except that dragons are obsessed with their hordes and territory. Taking some of it away--or worse, forfeiting it all--is terrifying for a dragon. Remember that most dragons have been collecting treasure for hundreds, even thousands of years.
Regardless the amount forfeited, the dragon is also subject to a period of banishment. During this time, other dragons are forbidden from dealing with them. They essentially become invisible. If the dragon attempts to force an interaction--by challenging another dragon during his time of banishment--he puts himself at risk for greater punishment, up to and including death.
But perhaps the worst punishment for a dragon is the knowledge that he's lost the respect of his or her fellows. Dragons are very particular about their reputations among other dragons. They don't really care much what anyone else thinks, but to lose face to other dragons is simply more humiliation that most dragons are willing to risk. That isn't to say they won't do it, it just means they have to be careful about it...and the reward has to be HUGE in proportion to the risk.
The following are examples of rules almost no dragon will violate, even under the worst circumstances:
- Damaging or destroying an unhatched egg.
- Killing a hatchling or the killing of a dragon in a clearly unfair fight.
- Using sorcery or technology to kill another dragon, even a superior one.
- Taking a formal position of authority over lesser races (i.e. humans).
- Excessive involvement in the affairs of lesser races.
- Killing a dragon who has already yielded.
- Stealing from another dragon's horde.
- Spending an extended period of time in another dragon's territory without asking permission.
