Q:

using .NET to emulate DTSExec /REP EWCDI

Using the library microsoft.sqlserver.dts.runtime.package is it possible to push an equivalent option used by DTEXEC (/REP EWCDI) from .NET to an SSIS package? ? 
(/REP EWCDI is a reporting feature of DTEXEC)

A:

The /REP command line option is a feature of DTEXEC.EXE.
DTEXEC is (conceptually) just a command line interface to the classes that enable executing an ssis package, which you already link to in your question.
When you use those classes to launch packages yourself, you need to provide the reporting functionality yourself too. This is done by creating a derived class the DefaultEvents class. In there you override all the OnError, OnInformation, etc. methods, redirecting the output where you want to have it (Console.Error for errors and warnings; Console.Out for other messages).
If you want to control what messages are output, like DTEXEC does by letting you specify the levels with the /REP option, you have to provide this yourself also. For example. By having respective flags/properties on your derived event class that you check in the On*-methods before actually printing the message.
Finally, if you want to have the exact same message format like DTEXEC (the "Begin Error" "End Error" blocks for example), you have to emulate that in your derived event class as well.
If is really not all that difficult to do as this MSDN page shows.

