Some states clearly state that, "an oversized mirror can replace a spotter,,,".
So check with your state to see if this is the case. No state that I know if allows "standard" size mirror to replace the spitter.
Many Sea Doos have factory installed "oversized" mirrors. Look up the spec sheet in your ski and if they are, it will say so on the sheet. Both of my skis have them for example.
When I lived in Ohio you still had to have a spotter AND the towing vehicle had to be able to carry all passengers legally.