Question: My party is about to enter a room full of enemies so I cast Spirit Guardians on myself designating my party as friendly. Our druid casts fog cloud or our warlock casts magical darkness in the room then I proceed to move through the fog or darkness using dodge as my action hoping to damage the enemy with the spirits.

Will the spirits be able to ignore the fog or darkness since they are spirits or will it hinder their attacks? If it does hinder their attacks, how so?

Answer: 
* You do not gain racial skill bonuses from the type of creature that you shapeshift into.
* In addition to the size modifiers to stats listed under the spell that you're mimicking with Wild Shape (ie, Beast Shape II, etc.), you also gain the standard size modifiers to attack, CMB, CMD, AC, and Stealth checks. If you are carrying a weapon and shapeshift into something that can wield that weapon (eg, using Giant Form), then the weapon grows or shrinks with you and its damage dice change. Your reach may also change. These size modifiers are not listed under the spells because they're part of the universal combat rules.
* You do not get the creature's BAB, saves, etc. The only attribute adjustments that you get are the ones listed under the spell that you're mimicking with Wild Shape.

Basically, if it's not part of the universal combat rules and it's not described under either Wild Shape or the spell that you're mimicking with it, you don't get it.
I would add that you also do not get special attacks/abilities from the form that are not explicitly listed under the "Wild Shape" spell. For example, Giant Toad has a swallow whole ability, but no level of Wild Shape lets you get that ability. So no swallow whole attack for you!