by "not-so-good ukemi" I mean that even though some 4th kyu in my dojo don't make fatal mistakes like landing on his hand or something, they still roll on their side rather than on their shoulder.. and by "roughly correct technique" I mean they still can't apply all the little details such as hands and feet positions and posture some of the times.. although, my dojo holds a kyu examination every 6 months so I guess our standards ARE supposed to be lower than you guys...
Both of those are serious flaws by 4th kyu.
By 4th kyu, IMO:
* free rolls -- without a partner -- should be good enough for brand new beginners to emulate.
* rolls from throws should be equally good, provided speed is moderate.
* at moderate speeds, student should be beginning to improvise ukemi from non-standard situations
* stances and basic footwork should be good enough for brand new beginners to emulate
* techniques within test requirements should be technically correct at moderate speeds, including footwork and hand positions
* student should be able to at least approximate new techniques as they are presented in class
* student should not completely fall apart under stress. If faced with a new or unexpectedly strong attack, they should have a better answer than "deer in headlights."
In our system, 4th kyu is the third test, and represents 9-12 months of consistent training. If you don't have people rolling correctly in a year I would be concerned about your teaching methodology.
Full disclosure: I teach beginners, but I do not personally supervise kyu tests or award rank. These are the criteria I look at when someone asks if they are ready.