Can Sql Server Backups be replaced by a netapp SnapManager?
Not at all. A SAN snapshot is a bitwise copy of raw disk state. If and only if all the responsibility for business continuity is on SAN storage team, this might be acceptable. For most of the business cases, this will present such RPOs and RTOs that the solution is not going to be feasible. What's more, restoring a SAN snapshot to a stable state is problematic. If the server was up and running during the snapshot, the server will return to state like someone hit a reset button. That is, a dirty filesystem, incomplete transactions and stuff. To get a clean snapshot, the server must be shut down a priori - and that's a business outage.

With SAN snapshotting only, you'd miss at least point in time recovery, as all the databases must be in simple recovery model due missing log backups. This is a killer for most recovery objectives.

Denny Cherry has written a whole article about failure points.