No you can not teach a pilot seeking their Instrument rating without a CFII. Notice what I said.
Procate pilot airplane requires 3 hours of instrument training. That can be taught by a CFI, doesn't need to be a CFII.
Also, if you work for a Part 135 operator and want to become an instructor and check pilot, you don't even need to be a CFI let alone a CFII. You will have to receive additional training particularly on the FOIs in that case. That said, most operators require their IPs to have at least a CFI. I teach tons of IFR each year with a 135 operator and don't have a CFI.
so the answer is no but there are exceptions like everything else.