.NET is under MIT license (https://github.com/Microsoft/dotnet/blob/master/LICENSE) and there's also a patent promise (https://msdn.microsoft.com/en-us/openspecifications/dn646766). There isn't an "enterprise .NET" version for sale. There are enterprise versions of Visual Studio, servers, etc., but nothing you could feasibly be "accidentally" using, and nothing that you have to use to do .NET dev.

What specific risk(s) are you thinking about?

Disclaimer: Microsoft employee, Nazgûl