Hi,
Like that, no.
When a user is logged as a vendor, he is nothing more than a normal user ; the vendor account is something near and it is only manage by HikaMarket.
HikaShop just see a regular account.
The only thing I can think about is a special user group.
After that, if the site crashes, you should have something in your PHP error log. And having an error could be more than useful to understand what is happening.
Because I can currently use my vendor accounts in my test websites to make orders in the front-end ; they can add products in there cart without any trouble.. That's why the source of your error is very difficult to understand.
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.