The core of mono is safe. It is covered under ECMA-334 (C# language) and ECMA-335 (CLIR vm). The mono MS Compatibility Stack, which includes:
- XML
- ASP.NET
- Windows.Forms
- ADO.NET
- Core cryptography
- Transactions
is a grey area now since the project is not part of Novell anymore. Novell and Microsoft had joint patent agreement, so there were no problems. So the question is, does wine-mono include the compatibility stack?
I know Windows.Forms is included. I'm not familiar with the other items, but if mono builds them by default then they're included.