Hello,
You can configure the category listing module to display sub elements and also to display itself in "simple ul/li" list.
Thanks to that, it is possible via CSS (and JS, if required) to customize the display and make the sub categories be visible on mouse hover.
Afterwards, you can find some plugins compatible with HikaShop like Maximenu CK which can handle HikaShop content in its menus.
It really depends on what you want to get at the end.
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.