Not really. If you provide backend access, you're probably giving more access already in other parts in Joomla. It's better to enable "frontend editing" in K2. This way, a user would only be able to modify their own content only. And you don't need to have a specific K2 category for them. Create a K2 User Group for them (call it for example "Bloggers" and assign permissions to a single category - call that "Bloggers" too for simplicity's sake). When users login to your site in the frontend, they will see controls to add content (via the K2 User module). They can then add content to that category only and see/edit only their items. To display these bloggers items in the frontend, just create menu items pointing to these K2 users.

K2 was built with contributing authors in mind since day 1.