This is definitely doable, but the procedure differs depending on the server model.
If you have the OpenManage application installed on the server, you can use it to reset the iDrac. Under the System node, Main System Chassis, you will see the iDrac in the hardware monitor list. One of the tabs for the iDrac node will have a reset option. The precise location varies by model and version of OpenManage installed, so just keep poking around until you find it.\
You can also do this from the command line. CD into the OpenManage directory and type:
racadm racreset soft
On my system, it's in C:\Program Files\Dell\SysMgt\rac5
For blade servers, you can open up the chassis's web console. Under Chassis Overview, go to the Troubleshooting tab. Select the blade you want to reset and choose "iDrac Reset" from the dropdown on the right, then hit Apply.
Also most rackmount server models have a physical button on the front of the chassis marked with a lower-case 'i'. On newer models, the button will be a blue light. On older ones, it's just a small gray button. Holding this button down for (~10 seconds?) will reset the Chassis Management Controller (CMC), of which the iDrac is a part. Some models just have a light with no button.
If all else fails, you can SSH into the iDrac via PuTTY or Telnet and issue the following command:
racreset soft
I got this all from Google, BTW. I've used the chassis console to do a reset before, but we've moved away from Dell in recent years so I can't find one with an iDrac right now to give more detailed info.