NDA on code-level support

No, quite the opposite. If they want, Apple can take your code and incorporate it into their own products. Or they can sell it to your competitors. This is why you must always create a minimal project that demonstrates your problem to send toe DTS, rather than submitting your real code.

See section 9.3 of the developer agreement:

9.3 Information Submitted to Apple Not Deemed Confidential

Apple works with many application and software developers and some of their products may be similar to or compete with Your Applications. Apple may also be developing its own similar or competing applications and products or may decide to do so in the future. To avoid potential misunderstandings and except as otherwise expressly set forth herein, Apple cannot agree, and expressly disclaims, any confidentiality obligations or use restrictions, express or implied, with respect to any information that You may provide in connection with this Agreement or the Program, including but not limited to information about Your Application, Licensed Application Information, and metadata (such disclosures will be referred to as “Licensee Disclosures”). You agree that any such Licensee Disclosures will be non-confidential. Except as otherwise expressly set forth herein, Apple will be free to use and disclose any Licensee Disclosures on an unrestricted basis without notifying or compensating You. You release Apple from all liability and obligations that may arise from the receipt, review, use, or disclosure of any portion of any Licensee Disclosures. Any physical materials You submit to Apple will become Apple property and Apple will have no obligation to return those materials to You or to certify their destruction.