Hi CBaker007,
iDRAC and OpenMange Essentials are really two completely different entities that each serve a different purpose. However, they also can be used together to create a server management solution.
First, check out this licensing white paper. Pages 6 & 7 outline the difference between Express licensing and Enterprise licensing.
en.community.dell.com/.../20067892.aspx
Second, OpenManage Essentials is a systems management console that provides simple, basic Dell hardware management and is available as a free download. Check out their link for more info:
www.delltechcenter.com/ome
Regarding your question about hardware monitoring and configuration, OME is basically an interface to the iDRAC (which is a dedicated service processor on each of your R720s) that performs the actual requested operations.
www.delltechcenter.com/idrac
Finally, Lifecycle Controller technology enables the ability to perform embedded management tasks without the need to install a software based agent ( like OME). It is tightly coupled with the iDRAC and is part of the dedicated service processor mentioned above.
www.delltechcenter.com/LC
I know this is a lot of information to absorb. Please respond if you have additional questions.
Regards,steve