What should be inspected when checking the hub oil seal?

A All of these.

explanation

Some hub oil seals will have a plastic or glass area, so you are able to tell that the oil is at the proper level. If there is not an area to view the oil, it will still need to be said. It will have several bolts, and they need to be tight and secure. Also, the seal needs to be in good condition and not leaking.