I heard back from Galaxy Desserts regarding their flash frozen croissants - only available through Williams-Sonoma mail order. Sadly, they are not nut-free.
Here is the company's response:
It is a really good question, and you were right to ask such information. Our croissants are NOT considered "nut free". We do offer croissants that do not contain any nuts however our products are manufactured in a facility that also processes tree nuts.
Too bad! But thanks to Galaxy for at least getting back to me with the information.