What do you consider “.net Help”? Help that’s launched by a .NET product?
DOTNET is proprietary to Flare and is an installed form of help. I suspect that you are not referring to that but needs to be covered in case.
At one time there were questions about .net and I believe the answer was that webhelp is just fine.
See www.grainge.org for RoboHelp and Authoring tips
I can also attest that one of my products is a VB .NET program and it works fine with locally-installed AIRHelp.
I've also created webhelp for a few .NET applications and it is a fine solution. Context Sensitive Help is breeze with .NET.