Somewhat surprisingly, the pool's still in perfect health.  I expect this vdev is relatively empty, which would help.  I've asked the vendor if they'll do an advance exchange on the drives, but I think I may order replacement (name brand) drives anyway, and burn in any replacements I get from the vendor and keep them as spares.  Seagate NAS 6 TB drives are $225 each at Newegg right now with a promo code, which doesn't sound too bad.