Hi,
Yes you can have both registration in the same time.
The HikaMarket registration can do "user + vendor" if the user is not logged or just "vendor" if the user already have an account (and is logged with it).
Depending that context, some element can be requested or not and the setting "usergroup on registration" will only be used with the "user + vendor" mode.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.