As for freezing - I would not think so, and I haven't been able to find anywhere that says otherwise.
People who are allergic to eggs are generally only sensitive to the yolk - the white does not cause them any problems. And, since you are only brushing on a minimal amount of an egg-white egg-wash as a binder to hold the sugar to the flowers you would not be consuming any great quantity.
You could possibly use whole milk in place of the egg-wash - don't know.
I did find this
recipe for egg-less crystallized violets - have no idea of how well it works.