Replying back to add further details in the event this thread is found in the future. A lun, while being a "disk" to a client that's connected to it, is just a file (using that very loosely here) on the volume itself. A share just exposes the volume to CIFS, making the volume capable of storing / accessing files over the CIFS protocol. So you can certainly have a volume that is used for both SAN or NAS (CIFS). HOWEVER, it's not recommended that you do that.
As a Best Practice you should use volumes housing LUNs only for SAN traffic and volumes for NAS related traffic only for NAS. Among other things, there is the issue of space accounting and space reservations that come into play for LUNs and if you are storing non-SAN data on the same volume as your NAS data it will make space accounting a nightmare
Marc
