Should be possible just like the other target languages by providing a different code generator. At least there are no show-stoppers yet from the VB language.
I'm not sure if will be possible for MR viewcomponents to work with VB. Last time I looked into this the language didn't support inline delegates with closure that the viewcomponent sections were built on in the csharp version. Hopefully that's not a problem - I doubt many people are using monorail from VB.NET web apps.
URL: http://sparkviewengine.codeplex.com/WorkItem/View.aspx?WorkItemId=2295