There is a huge amount of misleading information on whiskers on the web that HDG finishes are whisker free and that whiskers are caused by electroplating "stress". Various companies marketing groups have published all sort of unsubstantiated claims about HDG or pre-galvanized coating are zinc whisker free. Some company even claims that they don't have any recorded incidents of zinc whiskers of their zinc plated wire mesh cable trays. A great many people who have read the marketing of said companies and then subscribed to their statements as true.
While the rocket scientists at NASA have a VIDEO of whiskers on HDG coated steel here:
If you have trouble viewing the video at the link above, here are two documents showing zinc whiskers can grow on hot dipped galvanized steel pipe.
Zinc Whiskers on Hot Dip Galvanized Steel Pipe
SEM Investigation of Zinc Whiskers on Hot-dip Galvanized Coating and Bright Electroplated Coating.
Clearly, the only sure way to avoid zinc whiskers is to avoid zinc. In the case of wire basket cable tray, powder coating painted or manufactured from stainless steel is optimal. While there would be issue for powder coated cable trays considering grounding and electrical continuity. Thus the best answer is stainless steel. And we have a solution to use a special grade of stainless steel to make the cost more economical.