Does BTCMEX accept self-referrals?

No. Self-referrals are strictly prohibited.

The aim of an Affiliate Program is to encourage affiliates and ambassadors to spread the word about BTCMEX, not to get discounts for your own trading.

You must not undertake any deceptive or fraudulent methods to increase your Affiliate Reward, including but not limited to directly or indirectly, allow any of the invited Accounts to be: (i) an Account owned or controlled by you or a member of your immediate family or household, or (ii) an Account owned or controlled by a user who was already a BTCMEX user.