Good advice so far guys.
Most lower back injuries are a result of poor form, as the others have mentioned. The studies I have seen show that their is a similar risk to your lower back when using heavily weight vs. no weight. You are just as likely to injure you lower back bending down to tie your shoe as you are performing a heavy deadlift or squat. It's all about avoiding rounding and losing tension of the erectors. As your lower back rounds, the tension is lost and the stress of the exercise is shifted from the big erector muscles to the tiny ligaments, and intervertebral muscles of your spine. This is what causes injury.
I'm not really sure what Big BK means, by saying low back injuries are over rated, lol. Lower back injuries are no fun, and are a very common injury. I cringe every time I see someone working out incorrectly and sacrificing their lower back. They may be pain free now, but it's only a matter of time. Ligaments are notorious for taking a very long time to heal and one little slip up can mean a lifetime of back pain.
Hypers, and DB RDL's are a great starting point, and will build confidence. But if you are pain free now and are able to squat/dead with correct form then go for it. If you can't move with correct form, then stick to the hypers and work on fixing your flexibility problems.