What is the difference between monolithic and non-monolithic dc-dc converters?
Monolithic in the sense of the part you have refers to the fact that the power switch(es) is(are) integrated into the controller IC as a single part. There are cases when you have to purchase the switches as external components. 

In my opinion, a truly monolithic converter would be one that also integrates the inductor and possibly even the capacitors. I mean, look at all the stuff you have to add for the converter to work!