is there a good buttercream recipe that is okay for nut allergies?
I dont know of any buttercream recipes that use nuts but be sure to read every packet of every single thing you even think about adding.
Jason is the person for allergies and advice but if they have a severe allergy cross contamination, even utensils that have previously been in contact with nut products, may be a problem if you have previously baked with nuts.
I do not know of a recipe that uses nuts as an ingredient but, nuts can be added. Cross contamination can occur if you have made items containing nuts and can still result in an allergic reaction. I put my ingredients on a label and add to the bottom, "This product may contain, milk, eggs, wheat and nuts, or has been made in a location that has used these items."
Most BC recipes are fine...as said above you need to be very careful about cross contamination, both with your own baking processes and those of your suppliers. Check ingredient labels carefully, if the ingredients are processed on the same equipment as nuts you'll have to find another product, but depending on the severity of the allergy if they are only processed in the same facility as nuts the product may be OK if you contact the manufacturer and check on what their cleaning processes are.