The item should be labeled a page from a guide.
It should not be graded because was never intended to be a stand-alone item, unlike a W card.
Otherwise, I have no issue with accurately labeled items being slabbed. As long as they fit inside the slab it isn't my place to tell the submitter what to spend money on slabbing. I've had SGC slab a number of items that don't strictly conform to the ideal of a 'card'. I had them do this promo for a Benny Leonard play and it looks great:
I will have them do more of them when I think the item would be well preserved and displayed in a slab. I recently saw an auction [Goodwin?] that had an envelope from an early A's championship team in an SGC slab and I thought it looked great.