Do I need certified drives?

You can, but I wouldn't.

Here are some things you should know about drives:

1. Consumer/desktop/laptop drives.  These drives are designed for 8x5 operation and are programmed with settings to optimize them as being the only disk in a machine, with lax timings and long recovery thresholds.  These disks are generally unsuitable for use in RAID or enterprise storage devices.

You will almost surely experience issues with consumer drives ... anything from random offline/timeouts to not even being seen by the controller at all.

2. Enterprise drives.  These drives are designed for 24x7 operation and are programmed with settings to optimize them when used together with other disks in an array.  Timings and error and recovery thresholds are very small and very strict, with the assumption they would be used in a high-performance, redundant setup.  Enterprise drives are also programmed to respond to a different set of 'enterprise' commands that consumer disks are not.  Enterprise controllers expect drives to respond correctly and in a timely manner to these requests - consumer drives don't know how to respond to these requests at all; enterprise drives do.

You may or may not experience issues with retail/generic enterprise drives - it just depends on their settings and how closely they happen to match up to what the controller expects.  Generic/retail models typically have slightly more relaxed settings than certified drives, allowing them to be more generally compatible with more devices, but also possibly leading to issues communicating effectively with the controller.  Some drive manufacturers tweak and test their firmware to be compatible with various controllers.  Take the WD RE4, for example:  They have compatibility lists stating which controllers they have tested and verified compatibility with.  These are not considered "certified", in that the specific OEM has not approved the firmware, but there is a very high likelihood they will work without issue.

3. Certified drives.  These drives are enterprise class drives, but are loaded with a special version of firmware, tuned to the exact requirements and settings of the controller for which they are certified.  The settings and commands from the controller expect specific responses or expect responses in a particular timeframe, certified firmware ensures that regardless of the make or model of the drive, that drive is guaranteed to respond how and when the controller expects.  Certified firmware is loaded on the drives by the drive manufacturers for the OEM.  This is not a Dell practice - HP, IBM, and most of the big 'storage' names do this ... it is the only way to guarantee the reliability and performance of their systems.

All that said, as a recommendation/suggestion only, you can use "good" non-certified enterprise class drives OR certified drives, but I would not mix them if it can be helped.