I think that a cheater is someone who takes something that is supposed to be yours, i.e. a prize, a title, money, honors, etc., by dishonest means.

A deceiver is someone who intentionally misleads you.

A deceiver is a fraud of some sort. The word can be applied to anyone who makes false statements to sort of trick someone into believing something untrue. The verb is to deceive, the noun deception, or if pertaining to a person, a deceiver, although the word „deceiver“ doesn’t get a tremendous amount of use, it is possible. 

A cheater has a variety of possible applications. It`s often used with regard to games. One who cheats at a game, for instance, is one who doesn’t follow the rules of the game to win. It has a variety of other uses as well, unfaithfulness to someone with whom you are in an intimate relationship, like a spouse is the most common application of the word I would think. 

The difference is normally, as I see it, that a deceiver generates false information to gain some advantage, where a cheater betrays a rule, or someone`s trust, to attain a goal of some kind (like winning a game). These are just generalizations and I`d have to see a context in which either is used to see if it were being used properly.