So it looks like this is related to NULL values in the "is_deceased" field in CiviCRM. It looks like setting this value to 0 manually (using actual SQL) mitigated the issue. However, I'm not sure how to prevent this in the future other than perhaps explicitly setting the is_deceased on all of our bulk imports in the future.
Update This appears to be the same issue encountered in this thread: CiviMail Does Not Send To A Whole Group