If you try to ssh into user after installing openssh it'll ask you for a password. No matter what you enter, you won't be able to enter. Not even if you leave it blank.

As the above users have pointed out its because user has no password (now you would think if that's the case then it's just blank, no password right?). But nope, you can't log into user with any method if there's no password set for user.

You first have to get root access on the tablet and then set a password for user to be able to login as user (not sure about what if you try root since I always turn off root login).

And yes, if they ssh user into the device and do sudo gainroot they will have root access. Though if you setup openssh properly (strong password, change port #, and maybe even do some pub/private keys) you won't see what happened to jailbroken iPhones on the Nokia tablets.