Necro summoned pets will need two weapons to dual wield from pet level 19-32. At pet level 33+ the summoned pet does not need weapons to dual wield. Enabling dual wield on low level summoned pets or fighting summoned mobs (for the proc) would be the only reasons to give those summoned weapons to your summoned pet. That or you want your pet to look cool
[You must be logged in to view images. Log in or Register.]
Pets do not care about the delay of a weapon. They only care about the damage number. However, the damage number will only increase the pet's damage if the damage number x 2 is greater than the maximum hit damage for that pet. For example, if you gave a Tantors Tusk (50/60 weapon) to a summoned pet that normally does 40 damage maximum, you would increase the pet's maximum damage to 100 (50 x 2). Some weapons specifically have been nerfed to prevent the pet from using the damage number, such as the weighted axe (50/150 weapon that is easy to get). By the time you get to level 40, your pet will be hitting for up to 39. That excludes a large swath of cheap, easy to obtain weapons from being useful as pet weapons, as you would need a weapon with at least 20 damage to see any improvement.
Pets can proc weapons, but as mentioned above, ward summoned isn't a great proc for most encounters. There usually just aren't a lot of mobs flagged as summoned mobs.