1) Yes, it is okay to run RAM not on the QVL list. If your system is stable and running good don't worry about. The reason it is recommended to use the QVL, so you know the RAM has been certified to run at specified specs.
2) Yes, it is okay to run RAM at lower voltage and MHz... It doesn't cause issue with the RAM. You are just not running them at specification or what they are rated at (paid for). There are many that buy Cas9 DDR3 2000 memory but run it at Cas6 DDR3 1600 for the better timings (as an example).