I'm not a big fan of the View Control. I'm sure what you describe can be done but I'll offer an alternative approach.
I did this video showing a way to kinda of do a getSelectedIDs() from a repeat control (don't use IE):
http://xpages.tv/xtv3.nsf/episode_user.xsp?action=openDocument&documentId=94A
In that example the user could click on a row and I would add that ID to a map in sessionScope I think. Maybe viewScope - I forget. I used CSS to highlight the row to show it was selected. There was a button that removed the id from the map and refreshed to remove the highlight.
Now what you want to do - let's forget checkboxes for now. You should be able to use this repeat control technique then above your repeat have a button like Select all Pending. That button would run a SSJS function that would loop through your data on the backend and get the correct UNIDS and then add them to the map. A Partial refresh of the repeat would show them all selected. Another button that needs to act on the selected list would then just reference that map of the ID's.
Where I used css to highlight the row I imagine you could have a checkbox control and of that particular row was in the map - add the check, otherwise leave it empty.
Anyway - that's one way to approach it that you should be able to get working on short order.
Really if you're using a view control I guess you could still have a button that got the documents via the backend and do similar processing. In that case you might not need to add that check the the view since the selection is hard coded in reality. I guess the question is if you still need to mark them if you have that hard coded button.