Asking if certain materials were used is absolutely A-OK.
Also, if someone says they have an allergy, believe them. During the holidays an employee complained about the many poinsettias decorating our offices, allegedly due to his allergic reaction to that plant. My god, the way people scoffed. "They don't have a smell..." "Now I've heard everything...", etc., even from management! Except one manager, me. Never heard of such an allergy yet thought to research it to quell rising office conflict. Voila! Poinsettias are known allergens. Case closed. Poinsettias removed. There's more than one reason silk flowers were invented.