Yes. It is possible to signup as self registration in MikroTik RouterOS Hotspot.
And while self registration users can be verified with OTP sent via SMS & Email.
The only thing is that, you must edit the MikroTik default Hotspot Login Page. It can be accessible via FTP.
On MikroTik Hotspot Login Page, you have to a create HTML link for "New User Registration" which should be linked to your external webpage. (You must construct this your own).
There is a nice software package ( http://neucrm.com
) for Wifi Hotspot Self Signup with OTP. Please refer this link: http://neucrm.com/docs/Features/WiFi-Hotspot