Meh, the Union did not know any better what was in store than the South, and their cav was not off raiding - in fact, it was their cav that first refused the ridge to the South.
If Stuart had been around, Gettysburg does not really change. The errors made there were not driven by a lack of information, since the Union force was well screened anyway. Perhaps Lee would have done much of the same things in a more decisive manner, but I don't see the result changing really.
Geographically Buford's Union cavalry made their stand west north west of what developed into the entire battle, (the stand taking place at and just west of a line extending across Seminary Ridge, (not south of Gettysburg.)
Most historians agree that things would have been different had Lee been kept aware of the position of the Army of the Potomac, and a "shoe-hunting expedition" might not have evolved into the battle.
Buford served Meade better, than did Stuart for Lee, on this occasion.
No question that Stuart failed Lee, but I think the desire to hinge the outcome of the abttle on that failure is a bit of Lee apologism.
"Most historians" agree on a lot of things, and almost never on the things that people presume they agree on. I've read a rather lot about this battle, and would not agree that "most historians" pin its outcome on the lack of Stuart - he was one factor, but not the decisive one.
IMO, the decisive tactical factor was simply the terrain and interior Union lines. The decisive operational factor was Lee's insistence on fighting the Union army wherever it was found and his faith that if he could bring it to battle, under almost any circumstances, his boys could win. That resulted in him accepting a fight he should not have, and Stuart being there would not have changed that one bit - if anything, it would have made Lee even more over-confident in a poor tactical situation.