[Spinach]

Aside from the oft-mentioned Osgood & Niemi, every Cup winner since I can remember (the 80's) has had a clear-cut #1 or at least a reliable go-to guy if they weren't 100% sure, eg. the Caps last year, the Pens with Fleury/Murray.

The '84 Oilers had a platoon during the regular season, with close to an even split between Fuhr & Moog. Fuhr was the main starter in the playoffs, although Moog got into 7 games himself.

As for finalists, there are a few examples:
Philly in 2010,
The 2009 Wings who lost in the Finals had platooned Osgood & Conklin before rolling with Osgood
Philly in '97 (Snow/Hextall each saw significant time),
In 2002, the Canes platooned Barasso & Irbe, with Irbe winning the playoff starter role.

And that's without mentioning any semi-finalists.

So there aren't a plethora of examples of teams going far without a definitive #1, but there are enough to show it can be done if the team in front plays well. That's part of the beauty of the NHL postseason: you just never bloody well know!