According to what they say on the Ener-G website - Egg Replacer page - if you click on the "click here" information ... I would say probably not. It appears that it is for replacing eggs in baking - not in things like icings.
Q) What can you do and not do with the Egg Replacer?
Egg Replacer is used mainly in baking from scratch. Egg Replacer can be used with some commercial mixes but it is not recommended. Since there are no eggs or egg derivatives, it CANNOT be scrambled, hardboiled, etc
If you have to use a substitute (vegan, for example), you could try flax seed powder mixed with water. But I'm not sure how well it would work in your recipe and it won't taste the same.