This is the description from Greater Wildshape, but I imagine the druid wildshape applies the same way as the shifter greater version from NWN Wiki:
"Item merge:
Weapon is any melee weapon in the main hand slot.
Items are those in the ring slots, amulet slot, cloak slot, boots slot, or belt slot.
Armor is the item in the armor slot, plus a shield if in the off-hand slot and anything in the helmet slot.
The gloves or bracers slot and the ammunition slots never merge.
Rules of thumb:
Has a weapon? Merges all.
Unarmed, stands on two legs? Merges items & armor.
Unarmed, four or more legs? Merges armor only.
Exceptions to the rule are epic manticore, spectre, death slaad lord, stone golem, and demonflesh golem.
Because only the properties of the items are taken, and the item is "removed" and unavailable in the shifted form, any penalties from armor, such as penalties on skills, do not apply when shifted. This also means that a druid/shifter/monk who had been wearing armor or using a shield prior to shifting will have their special abilities reinstated because they will no longer be wearing armor or using a shield.
All AC bonuses become deflection bonuses, and only the highest applies.
If there are multiple bonuses to an ability score, only the highest applies. For example, if the shifter was wearing elven boots (+2 dexterity), a belt of agility +2 (+2 dexterity), and bracers of agility +3 (+3 dexterity), the final dexterity bonus on the shifted form is +2: the elven boots and belt of agility do not stack, and the bracers in the glove slot do not merge at all."
So it makes sense you don't get any bonus from the offhand weapon, since only the main slot merges into the shape for weapon.