It is not a safety issue to not blanch the cauliflower first, however the quality will probably be better if you blanch first and kill the enzymes that will affect the flavor and color of your end product.
Try it both ways and see what you like. I definitely would recommend blanching if you plan to store it for a long period of time. Cauliflower is a member of the Brassicaceae family. They tend to become strong flavored when frozen especially if not blanched.
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