Tim says:
How would I find out for sure whether the IC is a corporation or not?

Coach has the answer. [32a]

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32a:
Coach says:
Good question! Have the IC complete Form W-9, Request for Taxpayer Identification Number and Certification [32b]. On this form the IC will indicate his or her business status—sole proprietor, corporation, or partnership—as well as its EIN or SSN and address. (Both the business status and the EIN or SSN must appear on the 1099-MISC.)

Your 501(c)(3) should keep completed W-9s in its records and not send them to the IRS.

32b:
Form W-9, Request for Taxpayer Identification Number and Certification

Instructions for the Requester of Form W-9