For testing this, I blocked 204.28.125.162 (my own IP address at the time) in the Hebrew Wikipedia, with block ID #165352. I then logged in to my account, which has sysop permission in the Hebrew Wikipedia. I went to Special:CreateAccount, filled the form and submitted it. I saw a message saying that account creation from that IP is blocked.

I see no reason to prevent logged-in sysops from using account creation using Special:CreateAccount, even when account creation from that IP address is blocked. A sysop is supposed to be a trusted user who knows what he's doing, so it should be possible for a sysop to override the block.