This might be the way to do it although it is a real pain in C#.
Since the handlers are registered per instance, it isn't that difficult to tailor the functionality so that there is no need for that handle - i.e., it's obvious which tab generated the event.
the way you need to do this is as follows.
Depending on how you create the view it matters.
if you use IModelViewManager.CreateFeatureMgrWindowFromHandlex64. then you get the View Returned.
you can then register to the event with
AddHandler IFeatMgrView.ViewActivateNotify, addressof (SOME FUNCTION NAME)
then when you kill the view make sure you do
RemoveHandler Same as above.
the benefit here is that you will get calls specifically to this view. not all FeatMgrViews
alternatively you can get the handle to the FeatMgrView you created by
FeatMgrView.GetFeatMgrViewWnd and store that in a variable
then when the event is called
the View argument is an integer that matches the Handle you received from FeatMgrView.GetFeatMgrViewWnd
clear as mud?