Gauntlet as in "an attached weapon" can be targeted with spells that enhance weapons:
Player Guide p406 wrote:
They are still considered weapons and can be targeted as such by talents such as Disarm or Riposte, or by spells or abilities that target or enhance weapons.
Gauntlet as in the discipline, does not count as a weapon (normally) even if their friends lift them like a club.
However, both Claw Shape and Body Control include text like this:
Player Guide p134 wrote:
These are considered weapons for the purposes of targeting, though may not be removed by Disarm.
As for riposte the crucial bits are:
Player Guide p165 wrote:
The adept uses his melee weapon to block an opponent’s melee attack
Companion p103 wrote:
The adept can use Riposte against unarmed attacks, including creature attacks.
Note how it says "melee" instead of the usual "close combat", this coupled with the wording of the Claw Riposte knack (second quote) implies that Riposte can only be used against attacks that use the Melee Weapons talent/skill, not those that use Unarmed Combat