First of all, in this context "stealth" refers to technologies employed to evade detection by enemy sensors. It has nothing to do with crew size or a specific mission.
Second, Vengeance has a very small crew - much smaller than that of Enterprise. Enterprise, BTW, has more than a thousand crew.
On the scale of the Universe and of FTL travel, of course, there's no substantial difference in size between Enterprise, Vengeance or the Galileo 7 - they're all tiny.