Raw eggs are associated with salmonella, and some sources generally do not recommened them for use in smoothies. Others find the concern minimal as it is generally reported that only 1 in 30,000 eggs has a salmonella problem. Further, eggs from a high quality source are even less likely to contain salmonella. Look for paturized eggs, which are widely regarded as safe. Store bought egg substitutes can also be used.
Adding eggs to a smoothie adds protein and it is popular with low carb dieters and weightlifters. One large egg has 72 calories with almost all of that from protein and fat, so it is a definitely quality protein source.
To use egg in a smoothie, simply add it to the mix and blend. It is simple as that!