it's possible two ways. 1) you can use the internal system for vB to add users:
https://vborg.vbsupport.ru/showthrea...reate+New+User
that's a guide I found, but maybe you'll have better luck on getting it to work because I can't seem to. if you do get it working i'd love to know how :P
2) You can rebuild the whole registration system by hand, which requires advanced PHP/MySQL knowledge, but isn't to hard just more or less time consuming if you know what you're doing.