Pin properties in Diptrace
Although I have not used diptrace, I'll try to answer this question. I believe that the type adds a aesthetic characteristic to the symbol. For example adding a circle/bubble for inverted outputs or inputs, adding a > symbol to clock, etc. This is for display and readability purposes only.

On the other hand the electric parameter is used in the actual ERC. For example if the pin is defined as an input in the symbol, if it not connected in the schematic, flag has to be raised in ERC.

Further Reading: Inside OrCAD Capture for Windows By Chris Schroeder