generally, mississauga (where all spousal applications start) won't send an application back because a medical was not submitted up front. if it wasn't submitted upfront, it will be requested upon sponsor approval. many applicants do this without any issue.
reasons for applications to be sent back lately are because of missing forms, signatures, or outdated forms. they don't seem to be sent back because of missing medicals or police records. CIC tends to "look the other way" on these required documents because they don't have to do with the sponsor eligibility portion of the application, which is what mississauga is responsible for.