I don't think so. When people say that schools "screen," they generally don't mean that they read all the applications intensely and only send out secondaries to a select few. Generally, screening means that they have a minimum GPA and MCAT score, and you are screened out if yours are too low. These GPAs and MCAT scores are generally pretty low (aka, schools aren't setting their bottom thresholds at 3.6 and 33).
There are some schools who only send out secondaries to a select few. Those schools tend to only send secondaries to applicants they are inviting to interviews. Those schools will need your letters before they decide whether or not to interview you (and then send you a secondary). There aren't many schools like that, though.
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