Hi! Here is some code that will underline the drawing view labels. Should be a good starting point to do what you need. I did notice some strange side effects. For one, I did not expect hole callouts to be considered a DrawingViewLabel object. Second, after running this code any new views I placed automatically had underlined labels. Lastly, I don't think it works for Detail views, but the algorithm would be similar. Hope this helps!
Sub Main()
' Get current drawing. Assume a drawing is open
Dim drawing As Inventor.DrawingDocument = ThisDoc.Document
' Loop through all the views on the first sheet of the drawing
For Each view As Inventor.DrawingView In drawing.Sheets(1).DrawingViews
' Get the view label
Dim label As Inventor.DrawingViewLabel = View.Label
' Set the label style to be underlined
label.TextStyle.Underline = True
Next View
End Sub