Yes. But you'd need better decisions by Sigel in general, not just slaughtering the two hundred odd cadet battalion.
Sigel would have found some way to lose even if they hadn't shown up, from what I can tell.
Good idea for a POD, though - it isn't a huge deal, but it could seriously weaken Lee at precisely the wrong time as he tries to deal with it - not to mention that the two brigades (3,000 men?) he got from Breckinridge OTL...aren't coming.
