wiring dvc 4 ohm subs

1) no, unless you only use one voice coil and cut the available power in half.  This is not recommended unless you are an advanced user as it will also change all the T/S parameters of the driver and you will need to know how they change to construct your enclosure.  The ratings given by manufacturers are for both coils wired.

2) Nothing.  The amp will be happier and last longer.  It will produce about 1/2 of its 4-ohm rating.  Amps like higher impedence loads, they don't like lower impedence loads.