I don't believe the MD-series uses separate I/O queues for multiple LUNs. This only applies to Equallogic if I'm not mistaken.
So if everything will be presented to a single host or single hypervisor cluster, I don't think it'll make a difference other than the side-effects.
With the side-effects I mean that using multiple smaller LUNs means that 1 application cannot take diskspace away from another (possibly impacting the other application's functionality), but also means that one application cannot borrow space from another.