I see... outta my range of knowledge as far as LMCE goes, but theoretically as long as the LUNs are visible to LMCE, it should trigger the pnp process automatically to add them. I guess there are LUNs and there are LUNs (certainly in the SAN space this is the case, and how transparent they actually are can vary), perhaps they are not presenting to the OS in the way it is expecting.
You didn't say if they are SATA. If so, and there is no data on them, pull one out of the RAID and plug it directly into a SATA port as a standalone drive on the motherboard. Partition/format it - LMCE should detect it automatically, at least that will test if the pnp system is working properly for you. Maybe a case of a setting on the RAID controller to change how they present?
Gotta stop typing now, sorry - I broke both my hands 2 days ago and typing (pecking!) is extremely painful!