>Sure, why not - Irony is under MIT license, do whatever you want.
Actually I am considering Irony for a VB.NET and / or TSQL parser.
I am not yet on the StyleCop "team", but being bi-lingual C#/VB.NET and very appreciative of StyleCop, I am investigating writing/finding a VB.NET parser for styleCop.
>We have trouble - it crashes on parameters with default values, and gives up on entire project.
Are you able to post some sample code that illustrates this problem without disclosing any propriatry information? I would be glad to attempt to reproduce your problem and vote on it to be fixed.