Read more about Unschooling Curriculums, the custom DIY out-of-the-box curricula used by some unschoolers, because even some unschooling children respond well to the linguistic and logical learning styles preferred by schools and related institutions.
A frequently repeated bit of unschooling mythology includes the statement that unschoolers don't use educational materials or do any other activities that resemble school. Instead, they learn only what they can learn hands-on, without any instruction or guidance, in their everyday lives. From this misconception of unschooling comes questions such as "How will they learn calculus?"
In reality, unschoolers may use curriculum products if it makes sense to do so. My unschooling daughter does. If an unschooler wants to learn to read using a structured phonics program, they can buy or borrow one. If an unschooler wants to take a calculus class, they can do that, too. Or they can get their hands on a calculus text or instructional video and use that.
So, yes, of course unschoolers can use curricula. You don't expect their freedom-loving parents to tell them, "No," do you? The parent might even give some instruction. Unschooling parents do that, too.