I'll totally admit I'm not an expert on film making, but its still a Nolan movie. Remember, not only is he working on it, but the writer of TDK and Rises also wrote it with him (and wrote the screen play). Most of the producers are also from the Nolan BM movies. Its not just Nolan alone who is doing this, he has a whole Legion of Morons who are making this movie. By himself, he probably couldn't out influence Snyder. but, he has a lot of lackys on the movie, working in important roles.
Besides which, if Nolan did decide to not direct it, that probably means he helped pick snyder. As much as I'll give Snyder credit for working on a Watchmen movie that actually made the story something i could get through, he's probably a huge Nolan fan, and will do things Nolan's way. I won't go so far as to call him a puppet of Nolan or anything, but he's probably going to go with Nolan's style.