MRP view is not mandatory for any Material Type.
If your material is for planing SAP MRP process then you have to maintain MRP view for that material
and OMS2 will help you to maintain that view to respective material type
check following link you will get some idea
There is no One-to-One relationship between a material type and MRP. These are two distinct things. One which helps to classify a material, like (a Raw Material(ROH), Finished products (FERT)) and has its controlling features. [CLICK HERE TO KNOW ABOUT MATERIAL TYPE |http://help.sap.com/saphelp_46c/helpdata/en/ff/515afd49d811d182b80000e829fbfe/frameset.htm] ,whereas MRP helps in planning procure or produce material in an efficient way, where you keep inventory as low as you can yet meet all your requirements. [CLICK HERE TO READ MORE ABOUT MRP|http://help.sap.com/printdocu/core/print46c/en/data/pdf/ppmrp/ppmrp.pdf]
Hope this help.