Yes, you can configure it from backend > Easyblog > category > select your category > edit permission > select assign joomla user group option > select which user group you would like your user to post in this category, check my attached screenshot below.

Hope this help.

If still can't make it, can you provide us with your Joomla backend access at http://stackideas.com/dashboard/site so we can help you configure on this.