ADR 1/3 determine if the current IAS is in excess of 260 kias. If either detects that the speed is higher than this threshold, then a safety valve closes that prevents the gear from being extended until the speed drops below 260 kias.
If ADR 1 + 3 fail, then the 'high speed' signal would not be able to be sent to the safety valve. Airbus have foreseen this and have designed the system to close the safety valve if ADR 1 + 3 fail (see PRO ABN 34 NAV ADR 1 + 3 FAULT). Gear must be extended by gravity and retraction is not available.
I can't find anything conclusive, but would guess that in this circumstance, the gear could be extended at any speed by using the gravity gear extension handle.
The same would then apply to a full HYD, or ELEC failure. It seems that the gravity gear extension system overrides everything.