First, the problem of nitrosamine formation has never been found in MEA.  There is absolutely nothing to be concerned about with products containing MEA ingredients.
DEA ingredients can potentially react with other ingredients in the formula to produce nitrosamines which (in high enough doses) has been shown to be a carcinogen.
But what is the actual risk of getting cancer by using cosmetics that contain DEA?  No one knows for sure but in a governmental study done in 1998 (the National Toxicology Program) no link between exposure to DEA products and cancer in humans was established.  This doesn't prove that there is no risk, just that the risk is low to non-existent.
Their conclusion is "FDA believes that at the present time there is no reason for consumers to be alarmed based on the use of these substances in cosmetics."
Of course, when this topic made the rounds on the Internet back in the late 1990's, that scared most big manufacturers away from using DEA containing ingredients.  The only ones still using it are smaller brands who didn't want to go through the time and expense of creating new formulas.