Let me answer your questions one by one.
Question: Difference between VP-UML and SDE-VS.
You are right. The main difference is how they integrate with the IDE(s).
VP-UML can integrate with multiple Java IDE. It does not support Visual Studio.
SDE-VS, as suggested by the product name, can integrate with Visual Studio .NET (2003 and 2005).
Both VP-UML and SDE-VS supports round-trip engineering starting from the Professional Edition.
Question: Which one to choose?
If you are going to develop .NET application, I suggest you use the SDE-VS since it supports round-trip engineering with .NET languages (C++, C#, VB.NET) while VP-UML does not.
If you are going to develop Java application with Eclipse, both VP-UML and SDE-EC are suitable for you. Then which one to choose? The answer is depending on which way you want the UML environment to work with the coding environment.
The IDE Integration comes with VP-UML require running VP-UML and Eclipse in two separate windows, thus two separate VMs.
The integration comes with SDE for Eclipse runs the UML environment within Eclipse through the seamless integration. It acts as a plugin of Eclipse and it shares the same VM as Eclipse.
Question: C++ support for SDE-EC and SDE-NB
We are still planning the support of C++ for SDE-EC and SDE-NB. I will let you know once there are any news.
Question: Whats the difference in workflow, from user point of view,
Code Round-Trip Engineering (VP-UML Integration ) ?
If you are referring to the Instant Reverse for reverse engineering, the workflow is to select Tools menu and then Instant Reverse.
For round-trip engineering, you can update the code and model in several ways. Try right-click on the class code files (*.java within your Java project) and the code content, you should find the menu items for updating model from code. From the UML side, there are buttons in Diagram Navigator for you to update code from model. You can also select class models and then choose the update menu item from the pop-up menu to update code from model.
So the VP for UML Standard Edition just supports Reverse Engineering,
what’s the limit in comparison to code round-trip engineering, with your tools ?
The Standard Edition lets you reverse engineer your code base into UML class models, but not support code generation.
The Professional Edition supports both reverse engineering and code generation. There are two ways of reverse engineering. The first way is also the one supported by the Standard Edition, called Instant Reverse. For Instant Reverse, each reverse engineering process is a distinct one that overwrite changes to existing class models. The second way is through round-trip engineering, which merges the changes from code to model instead of overwriting.
I hope the information has helped. Please feel free to post again if there are any unsolved problems.