Voter Card is not mandatory for BHU UET Registration. As mentioned in their official website, an valid identification document is required. It could be PAN Card or Aadhaar card or Passport or Driving Licence or Voter Card or Bank passbook affixed with photograph or any other valid Government ID proof. Voter card is not the only ID proof. If you have Aadhaar card or PAN Card, then you can use that.